bug 5372: identify empty field in authority record correctly

bug 5372: identify empty field in authority record correctly

This is the sibling to the fix for this bug for the bib
editor.  However, note that this change won't have a
direct effect yet, as currently you can't specify a
default value for a field or subfield in the authority
MARC frameworks.  See bug 4887.

Signed-off-by: Galen Charlton <gmcharlt@gmail.com>
Signed-off-by: Chris Cormack <chrisc@catalyst.net.nz>
(cherry picked from commit daabd936d6cb13bd680652da5a32fd1ce354684a)

Signed-off-by: Chris Nighswonger <chris.nighswonger@gmail.com>