[BUGFIX] error with ve_guestbook

Resolves: #58447
Releases: 6.2, 4.7, 4.5
Change-Id: I57ef1e15a63bee92ab1d1072a78002d91d587e6c
Reviewed-on: https://review.typo3.org/29799
Reviewed-by: Ralf Zimmermann
Tested-by: Ralf Zimmermann