Fixing NPE in onFinishBindingItems (issue 10975740)

-> See bug for explanation. Seems like the circumstances leading to this
   NPE are understandable.

Change-Id: I89637a2da50be1081632e05cf79678c983a74d3a

src/com/android/launcher3/Launcher.java

@@ -915,7 +915,7 @@ public class Launcher extends Activity
     }
 
     protected void onFinishBindingItems() {
-        if (hasCustomContentToLeft() && mWorkspace.hasCustomContent()) {
+        if (mWorkspace != null && hasCustomContentToLeft() && mWorkspace.hasCustomContent()) {
             addCustomContentToLeft();
         }
     }