Invalid Resources-Path when TYPO3s Base-Url is a sub directory

When TYPO3s Base URL is a sub directory (not domain-root, eg. domain.de/my-cool-website) the path to the cookieOptIn.(css|js) file is wrong. It will be fetched from /fileadmin/sg_cookie_optin/siteroot-1/cookieOptin.css instead of /folder/fileadmin/sg_cookie_optin/siteroot-1/cookieOptin.css

Error occurs in v9.5

I've solved it by prefix the css/js with the configured Site-Base Classes/UserFunction/AddCookieOptinJsAndCss.php but this won't work in older typo3-versions.