[BUGFIX] Avoid undef array key in QueryGenerator

Just another sanitation in lowlevel QueryGenerator.

Resolves: #99568
Related: #98536
Releases: main, 11.5
Change-Id: Id7d8aa9856e7e148964bff0ef66e7c7b69bd6aaf
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/77414


Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: core-ci <typo3@b13.com>