[BUGFIX] Fix PHP 8 warning in ContentObjectRenderer

Added a guard around the calculation of $sameBeginEnd.

Resolves: #99752
Releases: main, 11.5
Change-Id: I754b4e67b2b04db20dc9adb8ee26bbd2ab2651ad
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/77581


Tested-by: Nikita Hovratov <nikita.h@live.de>
Reviewed-by: Nikita Hovratov <nikita.h@live.de>
Tested-by: core-ci <typo3@b13.com>