[CLEANUP] Replace count with empty in EXT:backend

Replace occurences of count() with matching empty() pendants.

Resolves: #67774
Releases: master
Change-Id: Ie75551a9410affe8840b521e15a0daf68655ba2a
Reviewed-on: http://review.typo3.org/40683


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