[FOLLOWUP][TASK] Doctrine: Migrate \TYPO3\CMS\Frontend\Page\PageRepository

The sorting field is optional and an empty field leads
to an invalid  query.

Resolves: #76543
Releases: master
Change-Id: I7e4e6c7ea873891b43d428d4db4a2d7ca63dc390
Reviewed-on: https://review.typo3.org/49456


Tested-by: Bamboo TYPO3com <info@typo3.com>
Reviewed-by: Mathias Schreiber <mathias.schreiber@wmdb.de>
Tested-by: Mathias Schreiber <mathias.schreiber@wmdb.de>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>