desktop-shell: Initialise panel surface listener

The desktop-shell output destroy code assumes that we always set up a
panel listener. Initialise its list explicitly, so if we don't have a
panel, then we can still unconditionally destroy the listener on output
destroy.

Signed-off-by: Daniel Stone <daniels@collabora.com>
Reviewed-by: Quentin Glidic <sardemff7+git@sardemff7.net>

desktop-shell/shell.c

@@ -4667,6 +4667,7 @@ create_shell_output(struct desktop_shell *shell,
 	shell_output->output = output;
 	shell_output->shell = shell;
 	shell_output->destroy_listener.notify = handle_output_destroy;
+	wl_list_init(&shell_output->panel_surface_listener.link);
 	wl_signal_add(&output->destroy_signal,
 		      &shell_output->destroy_listener);
 	wl_list_insert(shell->output_list.prev, &shell_output->link);