[BUGFIX] Also process array in InputSlugElement

It is possible that the incoming $row contains an array
at the $languageField. This patch assures that the
$languageId can always be determined.

Resolves: #86734
Resolves: #86554
Relates: #86754
Releases: master
Change-Id: Ia2c8621cd935788f33a9b625ec0226a22e21b123
Reviewed-on: https://review.typo3.org/58700


Reviewed-by: Susanne Moog <susanne.moog@typo3.org>
Tested-by: Susanne Moog <susanne.moog@typo3.org>
Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Oliver Hader <oliver.hader@typo3.org>
Tested-by: Oliver Hader <oliver.hader@typo3.org>
Reviewed-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Tested-by: Anja Leichsenring <aleichsenring@ab-softlab.de>