[TASK] Prevent superflous SQL queries in HMENU

When isSubMenu() decides, that the current page has no subpages, then do not try to fetch its subpages.

Resolves: #99657
Releases: main
Change-Id: I7f3395ad9caf17c3db3aaea7927b7bfb9acb924c
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/77519


Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: core-ci <typo3@b13.com>
Tested-by: Stefan Bürk <stefan@buerk.tech>
Tested-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Reviewed-by: Stefan Bürk <stefan@buerk.tech>
Reviewed-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>