Fix NPE in Workspace

Bug: 17503479
Change-Id: Ib20dfd67c5a755cd4b684163bb538a1bf77fa6ca
diff --git a/src/com/android/launcher3/Workspace.java b/src/com/android/launcher3/Workspace.java
index 909cf5f..051b0c0 100644
--- a/src/com/android/launcher3/Workspace.java
+++ b/src/com/android/launcher3/Workspace.java
@@ -1107,7 +1107,7 @@
         case MotionEvent.ACTION_UP:
             if (mTouchState == TOUCH_STATE_REST) {
                 final CellLayout currentPage = (CellLayout) getChildAt(mCurrentPage);
-                if (!currentPage.lastDownOnOccupiedCell()) {
+                if (currentPage != null && !currentPage.lastDownOnOccupiedCell()) {
                     onWallpaperTap(ev);
                 }
             }