[TASK] Do not output empty inDocStyles

If inDocStyles is empty, no output is needed.

Resolves: #63274
Releases: master
Change-Id: I886d6480231342ca6e505fabc801b7df6d899d53
Reviewed-on: http://review.typo3.org/34513
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>
Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Tested-by: Wouter Wolters <typo3@wouterwolters.nl>