[BUGFIX] Avoid PHP warnings in AbstractUserAuthentication

When dealing with 3rd-party authentication services,
which might return other values than arrays or
without UIDs.

This change fixes the relevant places.

Resolves: #95958
Releases: master
Change-Id: Idd50e3dceea079086a98225727ef7733a9b432c8
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/72157


Tested-by: core-ci <typo3@b13.com>
Tested-by: Oliver Bartsch <bo@cedev.de>
Tested-by: Georg Ringer <georg.ringer@gmail.com>
Reviewed-by: Oliver Bartsch <bo@cedev.de>
Reviewed-by: Oliver Klee <typo3-coding@oliverklee.de>
Reviewed-by: Georg Ringer <georg.ringer@gmail.com>