Bug 11416: fix case where serials item editor was incorrectly hiding fields

In serials/serials-edit.pl, if an item field is hidden from the OPAC,
it will not display in the editor, even if the field is marked as
visible in the staff intranet and editor. However, the field is still
displayed correctly in the items editor ( additem.pl ).:

Test Plan:
1) Select an item-level field ( e.g. non-public note )
2) Create a serial using the default framework ( or one of your choice )
3) For that framework, mark the chosen field as visible from the
intranet and editor, but not the opac.
4) Receive an item for this serial, note your field does not display
5) Use the biblio item editor to add an item ( additem.pl ), not the
field displayes
6) Apply this patch
7) Repeat step 4, not the field displayes

Signed-off-by: Kim Schwant <kim.schwant@courts.in.gov>
Signed-off-by: Jonathan Druart <jonathan.druart@biblibre.com>
PrepareItemrecordDisplay is only used for editor (-4 < hidden < 4)

Signed-off-by: Galen Charlton <gmc@esilibrary.com>