[BUGFIX] Scheduler tasks of deactivated exts should be considered invalid

If a scheduler task is created and the extension which provides the task is
deactivated the task must be shown as invalid in the list- and edit-view.

Change-Id: Iaf63c48c73ddaad64e153046d548eef5bbbcc7ae
Resolves: #68140
Releases: master
Reviewed-on: http://review.typo3.org/41246


Reviewed-by: Stefan Neufeind <typo3.neufeind@speedpartner.de>
Tested-by: Stefan Neufeind <typo3.neufeind@speedpartner.de>
Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Tested-by: Wouter Wolters <typo3@wouterwolters.nl>