[BUGFIX] Avoid validation failure on multi select fields without option

Multi Select fields without any option given will be added properly to
the forms __trustedProperties list and therefor no longer cause
validation errors.

Resolves: #90761
Releases: master, 9.5
Change-Id: I3c73ffbbd38a9a2ae24ed4b271efc1c4ce248d53
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/63720


Tested-by: TYPO3com <noreply@typo3.com>
Tested-by: Marco Huber <mail@marco-huber.de>
Tested-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Reviewed-by: Marco Huber <mail@marco-huber.de>
Reviewed-by: Anja Leichsenring <aleichsenring@ab-softlab.de>