Youtube JS still loaded even video field is blank.

On line 315 of bootstrap_carousel.module,

if (isset($slide['carousel_video'])) {
      drupal_add_js(variable_get('bootstrap_carousel_youtube_player_api', 'https://www.youtube.com/player_api'), 'external');
}

We should use empty function instead of isset like below.

if (!empty($slide['carousel_video'])) {
      drupal_add_js(variable_get('bootstrap_carousel_youtube_player_api', 'https://www.youtube.com/player_api'), 'external');
}