Clear notifications properly on ACTION_USER_STOPPED.

Which also takes care of the ACTION_USER_REMOVED case.

Bug:7277853
Change-Id: I0a6bade11bd0d420df03e16e69a386cfccfa07cc
diff --git a/services/java/com/android/server/NotificationManagerService.java b/services/java/com/android/server/NotificationManagerService.java
index 5d5f8d3..8d6c604 100755
--- a/services/java/com/android/server/NotificationManagerService.java
+++ b/services/java/com/android/server/NotificationManagerService.java
@@ -1240,7 +1240,7 @@
                 if ((r.notification.flags & mustNotHaveFlags) != 0) {
                     continue;
                 }
-                if (!r.pkg.equals(pkg)) {
+                if (pkg != null && !r.pkg.equals(pkg)) {
                     continue;
                 }
                 canceledSomething = true;