[BUGFIX] Avoid notice in template module by an early return

Return early in the template module on root page if a sys_template
record is retrieved from a page which itself is deleted.

Resolves: #103164
Releases: 11.5
Change-Id: Iabbf57d67559998819ad92829384b9d8b7ad1533
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/83049


Reviewed-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Tested-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Tested-by: core-ci <typo3@b13.com>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Ioulia Kondratovitch <ik@plan2.net>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>