Adding null check to prevent crash when factory resetting device. (5214968)

Change-Id: I514a17bdf097c6df17cacbe6d3aa59d427bc713b

src/com/android/launcher2/LauncherModel.java

@@ -588,7 +588,9 @@ public class LauncherModel extends BroadcastReceiver {
         } else if (SearchManager.INTENT_GLOBAL_SEARCH_ACTIVITY_CHANGED.equals(action) ||
                    SearchManager.INTENT_ACTION_SEARCHABLES_CHANGED.equals(action)) {
             Callbacks callbacks = mCallbacks.get();
-            callbacks.bindSearchablesChanged();
+            if (callbacks != null) {
+                callbacks.bindSearchablesChanged();
+            }
         }
     }