Bug 21222: (bug 20226 follow-up) Fix patron creation

Bug 21222: (bug 20226 follow-up) Fix patron creation

Since bug 20226 you cannot longer creation a patron, memberentry.pl will
explode with
Template process failed: undef error - DBIC result _type  isn't of the
_type Category at /home/vagrant/kohaclone/koha-tmpl/intranet-tmpl/prog/en/includes/str/members-menu.inc
line 22.

The problem is that "patron" is actually defined and the test in
str/members-menu.inc does not work as expected.

It comes from
  commit 7b1d08df0f4f69c52826c80a13158245287f4c00
  Bug 19936: Replace Generate_Userid - Update the occurrences
where I needed $patron to be defined in order to use Koha::Patron->generate_userid
on an blessed object.
But this was actually wrong, as it could have side-effects.

Test plan:
Create a new patron
Edit it
Retest bug 19936 and make sure the userid is generated correctly in the
different situations

Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>