[BUGFIX] Filename not displayed in selector (file_reference)

The selector values in BE-fields with type group->file_reference are
empty. The filename should be displayed at this place.

Resolves: #47414
Releases: 6.2, 6.1, 6.0
Change-Id: I9fa237d2cd14ff0e9b347736090bd2171eb8a747
Reviewed-on: https://review.typo3.org/23681
Reviewed-by: Anja Leichsenring
Tested-by: Anja Leichsenring