base: Fix NPE in GameManagerService

Change-Id: Id62b90dd37e6062792180cfdb19cb3a4fb371d3f
Signed-off-by: Pranav Vashi <neobuddy89@gmail.com>

Author: Dhina17

services/core/java/com/android/server/app/GameManagerService.java

@@ -2413,6 +2413,7 @@ class SettingsObserver extends ContentObserver {
         public void onChange(boolean selfChange, Uri uri) {
             String newValue = Settings.Secure.getString(mContentResolver,
                     "game_overlay");
+            if (newValue == null) return;
             // We write key and value of the device_config property as a single string
             // from our GameSpace.
             // ';;' is the separator betweeen key and value.