pass group mode to sub-galleries

    write_gallery(html_buf, "index.html", thumbnails, group=args.group)

    if args.group_files:

    if args.group_files != "none":

        thumbnail_keys = list(sorted(set(map(lambda t: t.file_key, thumbnails))))

        for thumbnail_key in thumbnail_keys:

            write_gallery(

                html_buf,

                f"{thumbnail_key}.html",

                list(filter(lambda t: t.file_key == thumbnail_key, thumbnails)),

                group=args.group,

            )