Bug 32426: Changes for members/memberentry.pl

Bug 32426: Changes for members/memberentry.pl

Test plan:
Note: We will address this again when installing a plugin, but
first we test with the legacy userid code.

Add a new user with members/memberentry in staff.
Edit this user, change userid in staff. Try full form and partial
one.
If you remove userid or replace by a space (when mandatory), Koha
should regenerate a legacy userid.

Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>