Bug 13757: (QA followup) Fix non-editable attrs on failed save

Bug 13757: (QA followup) Fix non-editable attrs on failed save

When a field is not editable but displayable in the OPAC, and you submit
an incomplete/wrong update, those attributes are displayed as empty.

This patch fixes that.

Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>