user32: When destroying a window, preserve the first WM_QUIT message that was posted to it.

dlls/user32/tests/msg.c

@@ -10241,7 +10241,7 @@ static void test_quit_message(void)
         add_message(&rmsg);
         DispatchMessage(&msg);
     }
-    ok_sequence(WmStopQuitSeq, "WmStopQuitSeq", TRUE);
+    ok_sequence(WmStopQuitSeq, "WmStopQuitSeq", FALSE);
 }
 
 static const struct message WmMouseHoverSeq[] = {

server/queue.c

@@ -1918,7 +1918,15 @@ void queue_cleanup_window( struct thread *thread, user_handle_t win )
         LIST_FOR_EACH_SAFE( ptr, next, &queue->msg_list[i] )
         {
             struct message *msg = LIST_ENTRY( ptr, struct message, entry );
-            if (msg->win == win) remove_queue_message( queue, msg, i );
+            if (msg->win == win)
+            {
+                if (msg->msg == WM_QUIT && !queue->quit_message)
+                {
+                    queue->quit_message = 1;
+                    queue->exit_code = msg->wparam;
+                }
+                remove_queue_message( queue, msg, i );
+            }
         }
     }