MDL-72915 qtype_ddimageortext: Fix eventHandler for Unlimited items

Sometimes, for the question that has a lot of input groups and unlimited draggable items,
the 'clone' process takes longer than usual, so the questionManager.init() method
will not add the eventHandler for the cloned drag.
We should make sure to bind the eventHandler for the cloned too

question/type/ddimageortext/amd/src/question.js

@@ -284,6 +284,11 @@ define(['jquery', 'core/dragdrop', 'core/key_codes'], function($, dragDrop, keys
                         cloneDrag.removeClass('beingdragged');
                         cloneDrag.removeAttr('tabindex');
                         hiddenDrag.after(cloneDrag);
+                        // Sometimes, for the question that has a lot of input groups and unlimited draggable items,
+                        // this 'clone' process takes longer than usual, so the questionManager.init() method
+                        // will not add the eventHandler for this cloned drag.
+                        // We need to make sure to add the eventHandler for the cloned drag too.
+                        questionManager.addEventHandlersToDrag(cloneDrag);
                     } else {
                         hiddenDrag.addClass('active');
                     }