Fix first render on Wayland after loading items with --grab

Currently, on the Wayland backend, the following command:
    { echo one; sleep 1; echo two; } | BEMENU_BACKEND=wayland bemenu --grab
Will keep showing the 'Loading...' text even after all items are available.
The items will only be shown after some input, e.g. a key press, happens.

This was a regression introduced by 5a09570
(versions 0.6.5+). A dirty flag was added to avoid unnecessary redraws,
however, this flag is not reset between the renders before/after the items are
loaded, so the bm_menu_render call after the items are loaded is ignored
(on Wayland, which is the only renderer that currently uses the dirty flag).

Fix the issue by resetting the flag after it is unset by the first grab render.

client/common/common.c

@@ -516,6 +516,7 @@ menu_with_options(struct client *client)
         // bm_menu_grab_keyboard(menu, true);
         bm_menu_render(menu);
         bm_menu_set_filter(menu, NULL);
+        menu->dirty = true; // Ensure a redraw on the first call to bm_menu_render after the items are loaded
     }
 
     return menu;