Fix PHP 8.1 deprecation

Hi,

the first strpos need to be patched too :

if ((strpos($path, '/webform/') === FALSE)
      || is_null($request)
      || is_null($request->getQueryString())
    ) {
      return $path;
    }

with the same solution

if ((strpos($path ?? '', '/webform/') === FALSE)
      || is_null($request)
      || is_null($request->getQueryString())
    ) {
      return $path;
    }

@Nicoc Please open a new ticket with your suggestion from #5.

Addressed