Don't allow showing an activity if user is stopping or shutting down.

BUG:29264996
Change-Id: I9fc97c5dc37e6d5656b82b277954b5963eb345c4
diff --git a/services/core/java/com/android/server/pm/UserManagerService.java b/services/core/java/com/android/server/pm/UserManagerService.java
index 4c515f0..d8a1c77 100644
--- a/services/core/java/com/android/server/pm/UserManagerService.java
+++ b/services/core/java/com/android/server/pm/UserManagerService.java
@@ -732,9 +732,9 @@
             long identity = Binder.clearCallingIdentity();
             try {
                 if (enableQuietMode) {
+                    ActivityManagerNative.getDefault().stopUser(userHandle, /* force */true, null);
                     LocalServices.getService(ActivityManagerInternal.class)
                             .killForegroundAppsForUser(userHandle);
-                    ActivityManagerNative.getDefault().stopUser(userHandle, /* force */true, null);
                 } else {
                     ActivityManagerNative.getDefault().startUserInBackground(userHandle);
                 }