PHP Fatal error: Using $this when not in object context

Hi @tbrehm The same error (and the same replacement by $username) like in issue #4486 (closed) but in different lines:

[Line 308] (https://git.ispconfig.org/ispconfig/ispconfig3/blob/2f12afd10d75ad5baaee55c0e703532e0d7de118/interface/web/login/index.php#L308) and [Line 319] (https://git.ispconfig.org/ispconfig/ispconfig3/blob/2f12afd10d75ad5baaee55c0e703532e0d7de118/interface/web/login/index.php#L319)