[CLEANUP] Replace count with empty in multiple extensions

Replace occurences of count() with matching empty() pendants.
Affected extensions:
- aboutmodules
- beuser
- compatibility6
- cshmanual
- css_styles_content
- dbal
- felogin
- sys_action
- t3editor
- taskcenter
- tstemplate

Resolves: #67777
Releases: master
Change-Id: I6986c71866c4f27f0c9bccc7d7d0dd14ea5695ac
Reviewed-on: http://review.typo3.org/40685


Reviewed-by: Markus Klein <markus.klein@typo3.org>
Tested-by: Markus Klein <markus.klein@typo3.org>
Reviewed-by: Stephan Großberndt <stephan@grossberndt.de>
Reviewed-by: Markus Sommer <markussom@posteo.de>
Reviewed-by: Stefan Neufeind <typo3.neufeind@speedpartner.de>
Tested-by: Stefan Neufeind <typo3.neufeind@speedpartner.de>