[BUGFIX] Fix undefined key warning in EXT:backend/history with PHP8

This fix a warning when you click on a Rollback (preview) button in history for pages or content elements.

Resolves: #96325
Releases: main, 11.5
Change-Id: Iec42cd04289a4c567840651686808b9ef43e1656
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/72615


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