Account for invisible borders when constraining modal dialogs

https://bugzilla.gnome.org/show_bug.cgi?id=656619

src/core/constraints.c

@@ -762,7 +762,7 @@ constrain_modal_dialog (MetaWindow         *window,
       y += parent->frame->rect.y;
 
       meta_frame_calc_borders (parent->frame, &borders);
-      y += borders.visible.top;
+      y += borders.total.top;
 
       y += info->borders->visible.top;
     }