support non-jpeg / non-rgb files (e.g. GIFs)

        f.write(main_css)

def create_thumbnail_html(index, filename, title):

def create_thumbnail_html(index, thumbname, filename, title):

    buf = """<div class="image-container">\n"""

    buf += f"""<a href="{filename}" class="glightbox" data-gallery="gallery1" data-description=".gdesc{index}">"""

    buf += f"""<img src=".thumbnails/{filename}" alt="{filename}" />"""

    buf += f"""<img src="{thumbname}" alt="{filename}" />"""

    buf += "</a>"

    buf += "</div>"

    buf += f"""<div class="glightbox-desc gdesc{index}">\n"""

        im = rotate_image(im, exif_tag)

        im.thumbnail((args.size * 2, args.size * 2))

        im.save(f".thumbnails/{filename}", "JPEG")

        html_buf += create_thumbnail_html(i, filename, format_exif(exif_tag))

        thumbname = f".thumbnails/{filename}"

        if not filename.lower().endswith((".jpeg", ".jpg")):

            thumbname += ".jpg"

        im.convert("RGB").save(thumbname, "JPEG")

        html_buf += create_thumbnail_html(i, thumbname, filename, format_exif(exif_tag))

    with open(f"{base_dir}/share/html_end", "r") as f:

        html_buf += f.read()