Handler::VNEdit: Fix bug with new staff/cast being removed on form error
Handler::VNEdit: Fix bug with new staff/cast being removed on form error

The names of the staff were fetched from the existing VN entry, so any
newly added staff were not present in that list, and would thus not
show up when the form validation failed.

This fix makes sure to always fetch the required data from the database.

erengy/vndb,christian-roggia/vndb,christian-roggia/vndb,christian-roggia/vndb,erengy/vndb,erengy/vndb