Fix 2583234 - It's ok for mCallbacks to be null.

Change-Id: Iec8df7b668a4657677f9c5421d00aa1b7df91015
diff --git a/src/com/android/launcher2/LauncherModel.java b/src/com/android/launcher2/LauncherModel.java
index 72675b9..5e1abe6 100644
--- a/src/com/android/launcher2/LauncherModel.java
+++ b/src/com/android/launcher2/LauncherModel.java
@@ -432,7 +432,7 @@
                     Log.d(TAG, "startLoader isLaunching=" + isLaunching);
                 }
                 // Don't bother to start the thread if we know it's not going to do anything
-                if (mCallbacks.get() != null) {
+                if (mCallbacks != null && mCallbacks.get() != null) {
                     LoaderThread oldThread = mLoaderThread;
                     if (oldThread != null) {
                         if (oldThread.isLaunching()) {
@@ -635,6 +635,10 @@
                         return null;
                     }
 
+                    if (mCallbacks == null) {
+                        return null;
+                    }
+
                     final Callbacks callbacks = mCallbacks.get();
                     if (callbacks != oldCallbacks) {
                         return null;