Protect against NPE while to updating service connection activities.

Bug: 28972558
Change-Id: I83f6e33248bb5b5c6ed34a3590d594bf82463a96
diff --git a/services/core/java/com/android/server/am/ActivityStackSupervisor.java b/services/core/java/com/android/server/am/ActivityStackSupervisor.java
index 01b2eb4..197d9ec 100644
--- a/services/core/java/com/android/server/am/ActivityStackSupervisor.java
+++ b/services/core/java/com/android/server/am/ActivityStackSupervisor.java
@@ -1338,7 +1338,9 @@
 
         // Update any services we are bound to that might care about whether
         // their client may have activities.
-        mService.mServices.updateServiceConnectionActivitiesLocked(r.app);
+        if (r.app != null) {
+            mService.mServices.updateServiceConnectionActivitiesLocked(r.app);
+        }
 
         return true;
     }