qxl: handle no updates in interface_update_area_complete

Simply return early in case there are no updated rects.
Signed-off-by: NGerd Hoffmann <kraxel@redhat.com>
Message-id: 1465395101-13580-1-git-send-email-kraxel@redhat.com

hw/display/qxl.c

@@ -893,7 +893,8 @@ static void interface_update_area_complete(QXLInstance *sin,
     int qxl_i;
 
     qemu_mutex_lock(&qxl->ssd.lock);
-    if (surface_id != 0 || !qxl->render_update_cookie_num) {
+    if (surface_id != 0 || !num_updated_rects ||
+        !qxl->render_update_cookie_num) {
         qemu_mutex_unlock(&qxl->ssd.lock);
         return;
     }