[BUGFIX] Fix notices in UserAuthentication

Resolves: #83003
Releases: master, 8.7
Change-Id: Iceaa7ab9bd436322229e591677c0aee16cd69f5c
Reviewed-on: https://review.typo3.org/54652


Reviewed-by: Markus Klein <markus.klein@typo3.org>
Tested-by: Markus Klein <markus.klein@typo3.org>
Reviewed-by: Susanne Moog <susanne.moog@typo3.org>
Tested-by: Susanne Moog <susanne.moog@typo3.org>
Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Stefan Neufeind <typo3.neufeind@speedpartner.de>
Tested-by: Stefan Neufeind <typo3.neufeind@speedpartner.de>