Preserve asleep disabled outputs in output config

mapnotify() stores the client's scene tree in client_surface(c)->data;
checkidleinhibitor() later reads it back as a wlr_scene_tree and calls
wlr_scene_node_coords() on it. unmapnotify() frees the scene tree with
wlr_scene_node_destroy() but leaves surface->data dangling, so the next
arrange() -> checkidleinhibitor() dereferences freed memory and crashes
(SIGSEGV) whenever an idle inhibitor outlives the unmap.

Reset the pointer to NULL on unmap so the existing !tree guard handles it.

dwl.c

@@ -1242,6 +1242,7 @@ void
 destroydecoration(struct wl_listener *listener, void *data)
 {
 	Client *c = wl_container_of(listener, c, destroy_decoration);
+	c->decoration = NULL;
 
 	wl_list_remove(&c->destroy_decoration.link);
 	wl_list_remove(&c->set_decoration_mode.link);
@@ -1347,6 +1348,10 @@ destroynotify(struct wl_listener *listener, void *data)
 		wl_list_remove(&c->map.link);
 		wl_list_remove(&c->unmap.link);
 		wl_list_remove(&c->maximize.link);
+		if (c->decoration) {
+			wl_list_remove(&c->set_decoration_mode.link);
+			wl_list_remove(&c->destroy_decoration.link);
+		}
 	}
 	free(c);
 }
@@ -2834,6 +2839,7 @@ unmapnotify(struct wl_listener *listener, void *data)
 	}
 
 	wlr_scene_node_destroy(&c->scene->node);
+	client_surface(c)->data = NULL;
 	printstatus();
 	motionnotify(0, NULL, 0, 0, 0, 0);
 }
@@ -2856,10 +2862,13 @@ updatemons(struct wl_listener *listener, void *data)
 
 	/* First remove from the layout the disabled monitors */
 	wl_list_for_each(m, &mons, link) {
-		if (m->wlr_output->enabled || m->asleep)
+		if (m->wlr_output->enabled)
 			continue;
 		config_head = wlr_output_configuration_head_v1_create(config, m->wlr_output);
 		config_head->state.enabled = 0;
+		if (m->asleep)
+			continue;
+
 		/* Remove this output from the layout to avoid cursor enter inside it */
 		wlr_output_layout_remove(output_layout, m->wlr_output);
 		closemon(m);