[BUGFIX] Avoid undef array key in SearchController

Resolves: #99572
Releases: main, 11.5
Change-Id: I65fe76b733b6b0fce9ebb7dd54759ae673ab1755
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/77418


Reviewed-by: Jasmina Ließmann <minapokhalo+typo3@gmail.com>
Tested-by: core-ci <typo3@b13.com>
Reviewed-by: Oliver Bartsch <bo@cedev.de>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Oliver Bartsch <bo@cedev.de>
Reviewed-by: Oliver Klee <typo3-coding@oliverklee.de>
Tested-by: Jasmina Ließmann <minapokhalo+typo3@gmail.com>
Tested-by: Benni Mack <benni@typo3.org>
Reviewed-by: Benni Mack <benni@typo3.org>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>