[BUGFIX] Prevent empty sorting field to be quoted and put into an array

Change-Id: I807a888ac7d977606d94f5ad9ccdfeee07ee61ec
Resolves: #82307
Releases: master, 8.7
Reviewed-on: https://review.typo3.org/53915


Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Sebastian Fischer <typo3@evoweb.de>
Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Reviewed-by: Oliver Hader <oliver.hader@typo3.org>
Tested-by: Oliver Hader <oliver.hader@typo3.org>