Fix bug with drag visualization and UserFolders.

When dragging an app shortcut, it was possible that we'd show a red rectangle
around a cell occupied by a UserFolder. This shouldn't be possible -- as soon
as that cell becomes the target drop cell, the folder should start handling
the drag and drop events.

Change-Id: I1b7a8b1aa9aeb7e2f1bd51ce8d947c06455e988f
diff --git a/src/com/android/launcher2/DeleteZone.java b/src/com/android/launcher2/DeleteZone.java
index 3a6c63d..b11b1dd 100644
--- a/src/com/android/launcher2/DeleteZone.java
+++ b/src/com/android/launcher2/DeleteZone.java
@@ -254,4 +254,10 @@
             return false;
         }
     }
+
+    @Override
+    public DropTarget getDropTargetDelegate(DragSource source, int x, int y, int xOffset, int yOffset,
+            DragView dragView, Object dragInfo) {
+        return null;
+    }
 }