[BUGFIX] Fix wrong validation of select fields in backend

This patch fix a wrong validation of select fields in backend.
Also some small performance imrpovements.

Resolves: #67794
Releases: master
Change-Id: Ic4a6335999f24ffcd112f255431c769b806d3014
Reviewed-on: http://review.typo3.org/40703


Reviewed-by: René Bigler <raziel@dunkelweiss.li>
Tested-by: René Bigler <raziel@dunkelweiss.li>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Tested-by: Anja Leichsenring <aleichsenring@ab-softlab.de>