kdb: PAC generator: do not fail if canonical principal is missing
    
    krbCanonicalName is mandatory for services but IPA services created
    before commit e6ff83e (FreeIPA 4.4.0, ~2016) had no normalization done
    to set krbCanonicalName; services created after that version were
    upgraded to do have krbCanonicalName.
    
    Accept krbPrincipalName alone since they have no alias either */
    
    Fixes: https://pagure.io/freeipa/issue/9465
    
    Signed-off-by: Alexander Bokovoy <abokovoy@redhat.com>
    Reviewed-By: Florence Blanc-Renaud <flo@redhat.com>
    Reviewed-By: Thierry Bordaz <tbordaz@redhat.com>