[BUGFIX] Avoid PHP array access error in workspaces

When a page with a content element that has images
assigned is copied in workspaces, a PHP array access
error is raised since sys_file_reference TCA has
no sortby ctrl.

Add an appropriate null fallback.

Resolves: #102231
Releases: main, 12.4, 11.5
Change-Id: I453a612a62a359156c8be2e087d1d121f1b9c3ea
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/81466


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