Fix NPE in Launcher onDestroy

Bug: 11765296
Change-Id: I83299656cc90b8a744afb0db4b5ea08675c8db82
diff --git a/src/com/android/launcher3/Launcher.java b/src/com/android/launcher3/Launcher.java
index ce6b20e..0a630fe 100644
--- a/src/com/android/launcher3/Launcher.java
+++ b/src/com/android/launcher3/Launcher.java
@@ -1877,7 +1877,7 @@
 
         mDragLayer.clearAllResizeFrames();
         ((ViewGroup) mWorkspace.getParent()).removeAllViews();
-        mWorkspace.removeAllViews();
+        mWorkspace.removeAllWorkspaceScreens();
         mWorkspace = null;
         mDragController = null;