forms: If an answer has no saved value, use the field

When processing the value of a DynamicFormEntryAnswer, if there is no
database-backed, value, then use the value of the associated field.
Merge pull request #1365 from greezybacon/issue/1326

forms: If an answer has no saved value, use the field

Reviewed-By: Peter Rotich <peter@osticket.com>