[FOLLOWUP][BUGFIX] Backend users: Exception in element browser with PHP 7

Resolves: #72767
Releases: master, 7.6
Change-Id: I0c585c0c50674aabf40aeec0af176bb34ad0edfd
Reviewed-on: https://review.typo3.org/46006


Reviewed-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Tested-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Reviewed-by: Georg Ringer <georg.ringer@gmail.com>
Tested-by: Georg Ringer <georg.ringer@gmail.com>