Bug 27626: Fix self registration if categorycode is hidden and PatronSelfRegistration...

Bug 27626: Fix self registration if categorycode is hidden and PatronSelfRegistrationVerifyByEmail

If categorycode is selected in
PatronSelfRegistrationBorrowerUnwantedField and
PatronSelfRegistrationVerifyByEmail is turned on, the patron self registration
fails with

   [You must provide a patron's category to validate password's strength
   and length] at /usr/share/perl5/Exception/Class/Base.pm line 88

Test plan:
0. Select categorycode in PatronSelfRegistrationBorrowerUnwantedField
   and turn on PatronSelfRegistrationVerifyByEmail
1. Self register a patron
2. Confirm that it works as expected with this patch applied.

Signed-off-by: Owen Leonard <oleonard@myacpl.org>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>