[BUGFIX] Check if value is array to prevent a PHP warning

Change-Id: I81dc99c9961ab817ad16a44c53f4c150e2bedba7
Resolves: #70423
Releases: master
Reviewed-on: http://review.typo3.org/43842


Reviewed-by: Ralf Zimmermann <ralf.zimmermann@tritum.de>
Tested-by: Ralf Zimmermann <ralf.zimmermann@tritum.de>
Reviewed-by: Bjoern Jacob <bjoern.jacob@tritum.de>
Tested-by: Bjoern Jacob <bjoern.jacob@tritum.de>
Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Tested-by: Wouter Wolters <typo3@wouterwolters.nl>