BluetoothTile: Avoid NPE during boot up phase

* Listening handling can only take place once mController
   is properly initialized.

Change-Id: Ice0c19321d8632bd55e1d403de95914ad53bad30

packages/SystemUI/src/com/android/systemui/qs/tiles/BluetoothTile.java

@@ -76,6 +76,7 @@ public class BluetoothTile extends QSTileImpl<BooleanState> {
 
     @Override
     public void handleSetListening(boolean listening) {
+        if (mController == null) return;
         if (listening) {
             mController.addCallback(mCallback);
         } else {