[BUGFIX] Outdated resource pointers crash for TCA type group

Using TCA type "group" with internal_type "folder" crashes in
the backend if existing resource pointers have been moved in
the filesystem (e.g. renamed or deleted).

Resolves: #81918
Releases: master, 8.7, 7.6
Change-Id: I1aadee90d1fe81cd821cc3df594351dbfc101482
Reviewed-on: https://review.typo3.org/53545


Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Benjamin Kluge <b.kluge@neusta.de>
Tested-by: Benjamin Kluge <b.kluge@neusta.de>
Reviewed-by: Henning Liebe <h.liebe@neusta.de>
Tested-by: Henning Liebe <h.liebe@neusta.de>
Reviewed-by: Susanne Moog <susanne.moog@typo3.org>
Tested-by: Susanne Moog <susanne.moog@typo3.org>