Fix #13818 by using more robust "find next carousel item" logic

js/carousel.js

@@ -63,6 +63,13 @@
     return this.$items.index(item || this.$active)
   }
 
+  Carousel.prototype.getItemForDirection = function (direction, active) {
+    var delta = direction == 'prev' ? -1 : 1
+    var activeIndex = this.getItemIndex(active)
+    var itemIndex = (activeIndex + delta) % this.$items.length
+    return $(this.$items[itemIndex])
+  }
+
   Carousel.prototype.to = function (pos) {
     var that        = this
     var activeIndex = this.getItemIndex(this.$active = this.$element.find('.item.active'))
@@ -100,7 +107,7 @@
 
   Carousel.prototype.slide = function (type, next) {
     var $active   = this.$element.find('.item.active')
-    var $next     = next || $active[type]()
+    var $next     = next || this.getItemForDirection(type, $active)
     var isCycling = this.interval
     var direction = type == 'next' ? 'left' : 'right'
     var fallback  = type == 'next' ? 'first' : 'last'