[BUGFIX] Fix undefined index and offset warning in lowlevel QueryGenerator

This patch fixes undefined index/offset warnings in ext:lowlevel
QueryGenerator using null coalescing operator.

Resolves: #95551
Releases: master
Change-Id: I26fd0bd77bdc086916a57460680b06de689134db
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/71521


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