LiveDisplayService: Catch NPE before LiveDisplayConfig is initialized

* During boot up phase the system is trying to update
   LiveDisplay tile status based on the applied mode.
   However, with LiveDisplayConfig not yet initialized this results
   in a NullPointerException. Address it and fallback to MODE_OFF.

Change-Id: I736da21455e74801aae69e16b9e80c8985b83a5a

lineage/lib/main/java/org/lineageos/platform/internal/display/LiveDisplayService.java

@@ -1,5 +1,6 @@
 /*
  * Copyright (C) 2016 The CyanogenMod Project
+ *               2019 The LineageOS Project
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -239,7 +240,7 @@ public class LiveDisplayService extends LineageSystemService {
 
         @Override
         public int getMode() {
-            if (mConfig.hasModeSupport()) {
+            if (mConfig != null && mConfig.hasModeSupport()) {
                 return mModeObserver.getMode();
             } else {
                 return MODE_OFF;