Allow create_notification outside handle_notify

This is a little bit wasteful but makes it safe to use notifications
created outside handle_notify without remembering to fill in all the
string fields.

dbus/xdg.c

@@ -113,15 +113,15 @@ static int handle_notify(sd_bus_message *msg, void *data,
 		return -1;
 	}
 
+	free(notif->app_name);
+	free(notif->app_icon);
+	free(notif->summary);
+	free(notif->body);
 	notif->app_name = strdup(app_name);
 	notif->app_icon = strdup(app_icon);
 	notif->summary = strdup(summary);
 	notif->body = strdup(body);
 
-	// These fields may not be filled, so make sure they're valid strings.
-	notif->category = strdup("");
-	notif->desktop_entry = strdup("");
-
 	ret = sd_bus_message_enter_container(msg, 'a', "s");
 	if (ret < 0) {
 		return ret;

notification.c

@@ -49,12 +49,13 @@ void reset_notification(struct mako_notification *notif) {
 		free(notif->image_data);
 	}
 
-	notif->app_name = NULL;
-	notif->app_icon = NULL;
-	notif->summary = NULL;
-	notif->body = NULL;
-	notif->category = NULL;
-	notif->desktop_entry = NULL;
+	notif->app_name = strdup("");
+	notif->app_icon = strdup("");
+	notif->summary = strdup("");
+	notif->body = strdup("");
+	notif->category = strdup("");
+	notif->desktop_entry = strdup("");
+
 	notif->image_data = NULL;
 
 	destroy_icon(notif->icon);
@@ -73,6 +74,7 @@ struct mako_notification *create_notification(struct mako_state *state) {
 	++state->last_id;
 	notif->id = state->last_id;
 	wl_list_init(&notif->actions);
+	wl_list_init(&notif->link);
 	reset_notification(notif);
 
 	// Start ungrouped.