Don't configure a window before it responds to _NET_WM_SYNC_REQUEST

In 97a4cc8c, we accidentally lost the check that kept us from
sending multiple configures to a window before it responds to
_NET_WM_SYNC_REQUEST. So _NET_WM_SYNC_REQUEST stopped working
properly. Add a check back with the same effect.

https://bugzilla.gnome.org/show_bug.cgi?id=696091

src/core/window.c

@@ -9413,6 +9413,15 @@ update_resize (MetaWindow *window,
       break;
     }
 
+#ifdef HAVE_XSYNC
+  /* If we're waiting for a request for _NET_WM_SYNC_REQUEST, we'll
+   * resize the window when the window responds, or when we time
+   * the response out.
+   */
+  if (window->sync_request_timeout_id != 0)
+    return;
+#endif
+
   if (!check_moveresize_frequency (window, &remaining) && !force)
     {
       /* we are ignoring an event here, so we schedule a