[TASK] Improve retrieving distribution list

If you open the "Get preconfigured distribution" extension manager
function the extension list is retrieved twice. Furthermore database
queries are executed multiple times. This patch improves retrieving the
extension list, prevents database queries and catches thrown errors to
prevent errors.

Releases: master, 6.2
Resolves: #66730
Change-Id: Ice1bd36e1233fde121bb33232f98a4e25480b0e0
Reviewed-on: http://review.typo3.org/39182


Reviewed-by: Helmut Hummel <helmut.hummel@typo3.org>
Tested-by: Helmut Hummel <helmut.hummel@typo3.org>
Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Reviewed-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Tested-by: Anja Leichsenring <aleichsenring@ab-softlab.de>