[BUGFIX] Prevent undefined array key in EXT:frontend classes

Resolves: #96816
Releases: main, 11.5
Change-Id: Id869a55136c6985e3fa609428099e5682c0eee12
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/73384


Tested-by: core-ci <typo3@b13.com>
Tested-by: Jochen <rothjochen@gmail.com>
Tested-by: Benni Mack <benni@typo3.org>
Tested-by: Oliver Bartsch <bo@cedev.de>
Reviewed-by: Jochen <rothjochen@gmail.com>
Reviewed-by: Achim Fritz <af@achimfritz.de>
Reviewed-by: Benni Mack <benni@typo3.org>
Reviewed-by: Oliver Bartsch <bo@cedev.de>