Fix subject display when a ChoiceField is used
Fix display of subject field for drop-down lists

There was a slight issue when transitioning from a short answer field to a
drop-down field, and when the CDATA table is dropped and rebuilt.
Merge pull request #1428 from greezybacon/issue/subject-dropdown

Fix subject display when a ChoiceField is used

Reviewed-By: Peter Rotich <peter@osticket.com>