[BUGFIX] Fix undefined index in ContentObjectRenderer

Like the surrounding $conf['max'], this array index access should also
be secured.

Releases: main, 11.5
Resolves: #97908
Change-Id: I36ad5cf3d9eac5655e8721c8913bed43ab26377f
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/75129


Reviewed-by: Oliver Klee <typo3-coding@oliverklee.de>
Reviewed-by: Benni Mack <benni@typo3.org>
Reviewed-by: Oliver Bartsch <bo@cedev.de>
Tested-by: core-ci <typo3@b13.com>
Tested-by: Benni Mack <benni@typo3.org>
Tested-by: Oliver Bartsch <bo@cedev.de>