Flickity Carousel disable custom navigation when reaching last slide

I'm currently using the Flickity Carousel to create a carousel with different film content panels.

The carousel is using a custom navigation to control it, rather than the standard one that comes with the carousel. However I'm struggling to disable the next navigation button when you reach the end of the carousel slides. Here is an example of what I'm trying to achieve and have based my code on this.

You will see from my example that the Previous button works correctly and is disabled when you first land on the carousel. However the Next button is never disabled when reaching the end.

Here is a JSFiddle

My code:

$(document).ready(function () {
  $('.carousel-container').each(function (i, container) {
        var options = {
            cellAlign:'left',
            groupCells:'3',
            pageDots: false,
            prevNextButtons: false
        };

        $('.carousel__slides').flickity(options);
        var $container = $(container);
        var $slider = $container.find('.carousel__slides');
        var flkty = $slider.data('flickity');
        var selectedIndex = flkty.selectedIndex;
        var slideCount = flkty.slides.length;
        var $prev = $container.find('.prev');
        var $next = $container.find('.next');

        // previous
        $prev.on('click', function () {
            $slider.flickity('previous');
        });

        // next
        $next.on('click', function () {
            $slider.flickity('next');
        });

        $slider.on( 'select.flickity', function() {

            // enable/disable previous/next buttons
            if ( !flkty.cells[ flkty.selectedIndex - 1 ] ) {
              $prev.attr( 'disabled', 'disabled' );
              $next.removeAttr('disabled'); // <-- remove disabled from the next
            } else if ( !flkty.cells[ flkty.selectedIndex +1 ] ) {
              $next.attr( 'disabled', 'disabled' );
              $prev.removeAttr('disabled'); //<-- remove disabled from the prev
            } else {
              $prev.removeAttr('disabled');
              $next.removeAttr('disabled');
            }
        });
    });
});

.carousel-container {
  position:relative;
  }

.carousel__slide {
  width: 20%;
  max-width:286px;
  opacity: 0.5;
    
}

.carousel__slide.is-selected {
  opacity: 1;
}


.carousel__nav {
  display:block;
}

.carousel__nav button {
  width:65px;
  height:50px;
  background:red;
  border-radius:0 100% 100% 0;
  position: absolute;
  top: 80px;
  cursor:pointer;
  border:none;
  outline:0;
  transition-duration: 0.3s;
  transition-property: all;
}

.carousel__nav button:hover,
.carousel__nav button:active,
.carousel__nav button:focus {
  background:green;
  outline:0;
}

.carousel__nav button:disabled {
  background:black;
   opacity: 0.5;
}

.carousel__nav button i {
  content:'';
  display:block;
  margin:0 auto;
  width: 0;
  height: 0;
  border-style: solid;
  border-width: 10.5px 0 10.5px 14px;
  border-color: transparent transparent transparent white;
}

.carousel__nav .prev {
  left:0;
}

.carousel__nav .prev i {
  transform:rotate(180deg);
}

.carousel__nav .next {
  right:0;
  border-radius:100% 0 0 100%;
}


.film-section {
  margin-top:50px;
}

.film-item {
  padding:0 15px;
}

.film-item p {
  font-size:1.4rem;
  line-height:2.6rem;
  margin-bottom:0;
}

.film-item__image {
    position:relative;
}

.film-item__play {
  width:65px;
  height:65px;
  border-radius:100% 0 0 0;
  position:absolute;
  right:0;
  bottom:0;
  background:rgba(0,0,0,0.4);
  border:none;
  transition-duration: 0.3s;
  transition-property: all;
}

.film-item__play:hover,
.film-item__play:active,
.film-item__play:focus {
    background:red;
    outline:0;
}

.film-item__play:after {
    content:'';
    display:block;
    margin:0 auto;
    width: 0;
    height: 0;
    border-style: solid;
    border-width: 10.5px 0 10.5px 14px;
    border-color: transparent transparent transparent white;
    position:absolute;
    top:31px;
    left:33px;
}

.heading-content {
    display:none;
    opacity: 0;
    visibility: hidden;
}

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<script src="https://unpkg.com/flickity@2/dist/flickity.pkgd.min.js"></script>
<link href="https://unpkg.com/flickity@2/dist/flickity.min.css" rel="stylesheet"/>

<div class="carousel-container">
  <div class="carousel__slides">
      <div class="carousel__slide">
        <div class="offset-slide"></div>
      </div>
      <div class="carousel__slide">
        <div class="film-item">
          <div class="film-item__image">
            <img class="w-100" src="http://placekitten.com/510/380" alt="">
          </div>
          <h3>Heading</h3>
          <p>Lorem ipsum dolor sit amet, consectetur adipiscing elit. Nunc volutpat augue at quam ultrices euismod vel ac sapien. Ut finibus posuere augue, eget condimentum nunc porttitor in. Praesent in ornare mi, at rhoncus felis. In iaculis viverra sem sit amet lacinia.</p>
        </div>
      </div>
      <div class="carousel__slide">
          <div class="film-item">
            <div class="film-item__image">
              <img class="w-100" src="http://placekitten.com/510/380" alt="">
            </div>
            <h3>Heading</h3>
            <p>Lorem ipsum dolor sit amet, consectetur adipiscing elit. Nunc volutpat augue at quam ultrices euismod vel ac sapien. Ut finibus posuere augue, eget condimentum nunc porttitor in. Praesent in ornare mi, at rhoncus felis. In iaculis viverra sem sit amet lacinia.</p>
          </div>
      </div>
      <div class="carousel__slide">
          <div class="film-item">
            <div class="film-item__image">
              <img class="w-100" src="http://placekitten.com/510/380" alt="">
            </div>
            <h3>Heading</h3>
            <p>Lorem ipsum dolor sit amet, consectetur adipiscing elit. Nunc volutpat augue at quam ultrices euismod vel ac sapien. Ut finibus posuere augue, eget condimentum nunc porttitor in. Praesent in ornare mi, at rhoncus felis. In iaculis viverra sem sit amet lacinia.</p>
          </div>
      </div>
      <div class="carousel__slide">
          <div class="film-item">
            <div class="film-item__image">
              <img class="w-100" src="http://placekitten.com/510/380" alt="">
            </div>
            <h3>Heading</h3>
            <p>Lorem ipsum dolor sit amet, consectetur adipiscing elit. Nunc volutpat augue at quam ultrices euismod vel ac sapien. Ut finibus posuere augue, eget condimentum nunc porttitor in. Praesent in ornare mi, at rhoncus felis. In iaculis viverra sem sit amet lacinia.</p>
          </div>
      </div>
      <div class="carousel__slide">
          <div class="film-item">
            <div class="film-item__image">
              <img class="w-100" src="http://placekitten.com/510/380" alt="">
            </div>
            <h3>Heading</h3>
            <p>Lorem ipsum dolor sit amet, consectetur adipiscing elit. Nunc volutpat augue at quam ultrices euismod vel ac sapien. Ut finibus posuere augue, eget condimentum nunc porttitor in. Praesent in ornare mi, at rhoncus felis. In iaculis viverra sem sit amet lacinia.</p>
          </div>
      </div>
      <div class="carousel__slide">
          <div class="film-item">
            <div class="film-item__image">
              <img class="w-100" src="http://placekitten.com/510/380" alt="">
            </div>
            <h3>Heading</h3>
            <p>Lorem ipsum dolor sit amet, consectetur adipiscing elit. Nunc volutpat augue at quam ultrices euismod vel ac sapien. Ut finibus posuere augue, eget condimentum nunc porttitor in. Praesent in ornare mi, at rhoncus felis. In iaculis viverra sem sit amet lacinia.</p>
          </div>
      </div>
      <div class="carousel__slide">
          <div class="film-item">
            <div class="film-item__image">
              <img class="w-100" src="http://placekitten.com/510/380" alt="">
              <h3 class="js-video-heading heading-content">Universitat Oberta de Catalunya</h3>
            </div>
            <h3>Heading</h3>
            <p>Lorem ipsum dolor sit amet, consectetur adipiscing elit. Nunc volutpat augue at quam ultrices euismod vel ac sapien. Ut finibus posuere augue, eget condimentum nunc porttitor in. Praesent in ornare mi, at rhoncus felis. In iaculis viverra sem sit amet lacinia.</p>
          </div>
      </div>
      <div class="carousel__slide">
          <div class="film-item">
            <div class="film-item__image">
              <img class="w-100" src="http://placekitten.com/510/380" alt="">
            </div>
            <h3>Heading</h3>
            <p>Lorem ipsum dolor sit amet, consectetur adipiscing elit. Nunc volutpat augue at quam ultrices euismod vel ac sapien. Ut finibus posuere augue, eget condimentum nunc porttitor in. Praesent in ornare mi, at rhoncus felis. In iaculis viverra sem sit amet lacinia.</p>
          </div>
      </div>
      <div class="carousel__slide">
          <div class="film-item">
            <div class="film-item__image">
              <img class="w-100" src="http://placekitten.com/510/380" alt="">
            </div>
            <h3>Heading</h3>
            <p>Lorem ipsum dolor sit amet, consectetur adipiscing elit. Nunc volutpat augue at quam ultrices euismod vel ac sapien. Ut finibus posuere augue, eget condimentum nunc porttitor in. Praesent in ornare mi, at rhoncus felis. In iaculis viverra sem sit amet lacinia.</p>
          </div>
      </div>
      <div class="carousel__slide">
        <div class="offset-slide"></div>
      </div>
  </div>
  <div class="carousel__nav">
    <button class="prev" disabled><i></i></button>
    <button class="next"><i></i></button>
  </div>
</div>

from Flickity Carousel disable custom navigation when reaching last slide