[BUGFIX] Exception when hiding a File Reference

Change-Id: I089693c7c7280d385ae653ad7d9a9432c6dc1c38
Releases: 3.2
Resolves: #62370
Reviewed-on: http://review.typo3.org/33410
Reviewed-by: Fabien Udriot <fabien.udriot@ecodev.ch>
Tested-by: Fabien Udriot <fabien.udriot@ecodev.ch>