[SEC] installer: Check prefs before filtering user input. Changes filtering logic added in r50025

git-svn-id: file:///var/local/code.tiki.org/tikisvn/branches/12.x@50037 b456876b-0849-0410-b77d-98878d47e9d5
[MRG] Automatic merge, branches/12.x 50026 to 50037

git-svn-id: file:///var/local/code.tiki.org/tikisvn/trunk@50041 b456876b-0849-0410-b77d-98878d47e9d5