Bug 6022: Auth_with_ldap check if categorycode is valid

Bug 6022: Auth_with_ldap check if categorycode is valid

When importing users from LDAP, Auth_with_ldap.pm doesn't check if value for
categorycode is present in categories table in Koha resulting in referential
integrity error instead of using default value from koha-conf.xml

Test scenario:
1. enable LDAP in koha-conf.xml using <useldapserver>1</useldapserver>
   and add <ldapserver> configuration with
   <categorycode is="SomeLDAPField">DefaultCategoryCode</categorycode>
2. select/create LDAP user with category in SomeLDAPField which isn't in
   Koha
3. try logging in and ensure that assigned category to new user is
   DefaultCategoryCode

Signed-off-by: Marijana Glavica <mglavica@ffzg.hr>
Signed-off-by: Paul Poulain <paul.poulain@biblibre.com>