Bug 13757: (QA followup) Exclude empty attributes from rendering if non-editable

Bug 13757: (QA followup) Exclude empty attributes from rendering if non-editable

In self registration opac displayable (and not editable) attributes are
displayed as empty. This an empty value is passed to the template for
creating an empty input and it shouldn't when the attribute is not
editable.

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