Bugfix: Correctly unmap stack windows and don’t re-map them too early

src/client.c

@@ -39,9 +39,11 @@ void client_remove_from_container(xcb_connection_t *conn, Client *client, Contai
         /* If the container will be empty now and is in stacking mode, we need to
            unmap the stack_win */
         if (CIRCLEQ_EMPTY(&(container->clients)) && container->mode == MODE_STACK) {
+                LOG("Unmapping stack window\n");
                 struct Stack_Window *stack_win = &(container->stack_win);
                 stack_win->rect.height = 0;
                 xcb_unmap_window(conn, stack_win->window);
+                xcb_flush(conn);
         }
 }