Bug 24892: Resolve uninitialized warns from opac-memberentry

Bug 24892: Resolve uninitialized warns from opac-memberentry

Especially line 500 (current master).

Use of uninitialized value $new_data{"sort2"} in string eq at /usr/share/koha/opac/opac-memberentry.pl line 500.
Use of uninitialized value in string eq at /usr/share/koha/opac/opac-memberentry.pl line 500.

Simple fix, not completely trivial due to adding xor ;)

Test plan:
Do not apply, update from opac memberentry. Check warns in log.
Apply patch, update again. Less warns?

Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Owen Leonard <oleonard@myacpl.org>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>