window-props: Fix frame update on hide-titlebar-when-maximized changes

Since we started caching frame borders in commit b4036e061, we need to
invalidate the cache for changes of the GTK_HIDE_TITLEBAR_WHEN_MAXIMIZED
property to take effect immediately.

https://bugzilla.gnome.org/show_bug.cgi?id=781862

src/x11/window-props.c

@@ -1721,6 +1721,7 @@ reload_gtk_hide_titlebar_when_maximized (MetaWindow    *window,
   if (META_WINDOW_MAXIMIZED (window))
     {
       meta_window_queue (window, META_QUEUE_MOVE_RESIZE);
+      meta_window_frame_size_changed (window);
 
       if (window->frame)
         meta_frame_update_style (window->frame);