[BUGFIX] PHP warnings and empty authentication errors in log

Fixes: #60932
Change-Id: Ie7465d0f31dcec843c903548147447e261e156c6
Reviewed-on: http://review.typo3.org/32141
Reviewed-by: Thierry Brodard <thierry.brodard@techniconcept.ch>
Tested-by: Thierry Brodard <thierry.brodard@techniconcept.ch>
Reviewed-by: Xavier Perseguers <xavier@typo3.org>
Tested-by: Xavier Perseguers <xavier@typo3.org>