[TASK] Introduce early returns in DataHandler::canDeletePage()

Change-Id: Ib73136e767ee1fa8b97684a3cf03f763db8d907e
Resolves: #68775
Releases: master
Reviewed-on: http://review.typo3.org/42296


Reviewed-by: Daniel Maier <dani-maier@gmx.de>
Tested-by: Daniel Maier <dani-maier@gmx.de>
Reviewed-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Tested-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Reviewed-by: Andreas Wolf <andreas.wolf@typo3.org>
Tested-by: Andreas Wolf <andreas.wolf@typo3.org>