fix NPE in updateClientUids

Bug: 8009908
Change-Id: I54d97c587a3fa9d003f654f98fdfdbe21af791d6
diff --git a/services/java/com/android/server/location/GpsLocationProvider.java b/services/java/com/android/server/location/GpsLocationProvider.java
index 0c54d5a..12c14bf 100644
--- a/services/java/com/android/server/location/GpsLocationProvider.java
+++ b/services/java/com/android/server/location/GpsLocationProvider.java
@@ -858,6 +858,9 @@
     private void updateClientUids(WorkSource source) {
         // Update work source.
         WorkSource[] changes = mClientSource.setReturningDiffs(source);
+        if (changes == null) {
+            return;
+        }
         WorkSource newWork = changes[0];
         WorkSource goneWork = changes[1];