Driver GdImage : supports more image types

[MKCG]

GdImage::createImageDescriptor( throws an Exception when it can not determine the number of channels used by the image to encode.

switch (mime_content_type($filepath)) {
    case "image/jpeg":
        break;

    case "image/png":
        $marker = file_get_contents($filepath, false, null, 25, 1);
        $channels = match(ord($marker)) {
            2, 3 => 3,
            6 => 4,
            default => throw new DriverException(),
        };

        break;

    case "image/webp":
    default: throw new DriverException();
}