Fixing issue with cancelled drag blocking cell spaces (Issue 5386523)

Change-Id: I9cfc728edeeee2237c21935517107e7a2af49646

src/com/android/launcher2/DropTarget.java

@@ -52,6 +52,9 @@ public interface DropTarget {
         /** Post drag animation runnable */
         public Runnable postAnimationRunnable = null;
 
+        /** Indicates that the drag operation was cancelled */
+        public boolean cancelled = false;
+
         public DragObject() {
         }
     }