[TASK] Avoid possibly undefined variables

phpstan identified a bunch of possibly undefined
variables which is fixed with this patch.

Releases: master
Resolves: #90581
Change-Id: If41bee3dcd972d26f8eff18dbcbc61ad1fe79e7f
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/63483


Tested-by: TYPO3com <noreply@typo3.com>
Tested-by: Frank Nägler <frank.naegler@typo3.org>
Tested-by: Andreas Fernandez <a.fernandez@scripting-base.de>
Reviewed-by: Guido Schmechel <guido.schmechel@brandung.de>
Reviewed-by: Oliver Klee <typo3-coding@oliverklee.de>
Reviewed-by: Frank Nägler <frank.naegler@typo3.org>
Reviewed-by: Andreas Fernandez <a.fernandez@scripting-base.de>