[BUGFIX] Allow setting standalone modules as start module

Resolves: #90864
Releases: master
Change-Id: I3936c3a0c51f8bd05a6388f07240fe0e7d530779
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/63997


Tested-by: Richard Haeser <richard@maxserv.com>
Tested-by: TYPO3com <noreply@typo3.com>
Tested-by: Georg Ringer <georg.ringer@gmail.com>
Reviewed-by: Richard Haeser <richard@maxserv.com>
Reviewed-by: Georg Ringer <georg.ringer@gmail.com>