[BUGFIX] Fix page position selector on root page

Ensure the "new record" page position selector works
on the root page (pid 0).

Resolves: #96883
Releases: main, 11.5
Change-Id: I25681e5b0a2608dde3ca47180f443820cd7ff5bc
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/73481


Tested-by: Benjamin Franzke <bfr@qbus.de>
Tested-by: core-ci <typo3@b13.com>
Tested-by: Oliver Bartsch <bo@cedev.de>
Reviewed-by: Benjamin Franzke <bfr@qbus.de>
Reviewed-by: Oliver Bartsch <bo@cedev.de>