[BUGFIX] Avoid undefined array key in PageRepository

Resolves: #98404
Releases: main, 11.5
Change-Id: I01f52c45d95f6ff2a56e0a3128f1367dc2a595aa
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/76061


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