We need define global const for webp-express folder

[gerasart]

Hi, that better works with code and forgot about some special logic for user, we need add const like

define( ' WEBP_EXPRESS_UPLOAD_FOLDER' )

wp-content/plugins/webp-express/lib/classes/Paths.php:376

    public static function getWebPExpressContentDirAbs()
    {
        return self::getContentDirAbs() . '/webp-express';
    }

because for now plugin can save files just in wp-content folder.