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

Change-Id: I514a17bdf097c6df17cacbe6d3aa59d427bc713b
diff --git a/src/com/android/launcher2/LauncherModel.java b/src/com/android/launcher2/LauncherModel.java
index 21c34bb..060bd66 100644
--- a/src/com/android/launcher2/LauncherModel.java
+++ b/src/com/android/launcher2/LauncherModel.java
@@ -588,7 +588,9 @@
         } 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();
+            }
         }
     }