Add a missing NULL check for postActivityStartTokenRemoval()

* filter.receiverList.app can actually be null here. Don't pass
   a null ProcessRecord to postActivityStartTokenRemoval().

Change-Id: I923f424fcb05b3956bf14728e9d0c0e48666294d

services/core/java/com/android/server/am/BroadcastQueue.java

@@ -809,7 +809,8 @@ public final class BroadcastQueue {
                         r.resultExtras, r.ordered, r.initialSticky, r.userId);
                 // parallel broadcasts are fire-and-forget, not bookended by a call to
                 // finishReceiverLocked(), so we manage their activity-start token here
-                if (r.allowBackgroundActivityStarts && !r.ordered) {
+                if (filter.receiverList.app != null
+                        && r.allowBackgroundActivityStarts && !r.ordered) {
                     postActivityStartTokenRemoval(filter.receiverList.app, r);
                 }
             }