[BUGFIX] Fix PHP 8 warning in PageRepository

Added Null coalescing operator, when value of $row['uid'] and
$row['pid'] is accessed in getRecordOverlay to avoid PHP
warning.

Resolves: #99993
Releases: main, 11.5
Change-Id: Ia5b9983f6679001734b81bbd4a56d697bb3ce454
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/77907


Tested-by: core-ci <typo3@b13.com>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Oliver Bartsch <bo@cedev.de>
Reviewed-by: Oliver Bartsch <bo@cedev.de>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Stefan Bürk <stefan@buerk.tech>
Reviewed-by: Stefan Bürk <stefan@buerk.tech>
Reviewed-by: Oliver Klee <typo3-coding@oliverklee.de>