Don't crash if there's no bluetooth functionality (such as in an emulator)

Bug: 6079494
Change-Id: I12f729134407eaa719dc6a25e89a3b48476985e2

src/com/android/settings/bluetooth/DeviceListPreferenceFragment.java

@@ -96,6 +96,7 @@ public abstract class DeviceListPreferenceFragment extends
     @Override
     public void onResume() {
         super.onResume();
+        if (mLocalManager == null) return;
 
         mLocalManager.setForegroundActivity(getActivity());
         mLocalManager.getEventManager().registerCallback(this);
@@ -106,6 +107,8 @@ public abstract class DeviceListPreferenceFragment extends
     @Override
     public void onPause() {
         super.onPause();
+        if (mLocalManager == null) return;
+
         removeAllDevices();
         mLocalManager.setForegroundActivity(null);
         mLocalManager.getEventManager().unregisterCallback(this);