sidgen: ignore staged users when generating SIDs
    
    Staged users have
    
      uidNumber: -1
      gidNumber: -1
      ipaUniqueID: autogenerate
    
    We cannot generate ipaSecurityIdentifier based on those UID/GID numbers.
    However, '-1' value will trigger an error
    
     find_sid_for_ldap_entry - [file ipa_sidgen_common.c, line 483]: ID value too large.
    
    And that, in turn, will cause stopping SID generation for all users.
    
    Detect 'ipaUniqueID: autogenerate' situation and ignore these entries.
    
    Fixes: https://pagure.io/freeipa/issue/9517
    
    Signed-off-by: Alexander Bokovoy <abokovoy@redhat.com>
    Reviewed-By: Florence Blanc-Renaud <flo@redhat.com>
    Reviewed-By: Thierry Bordaz <tbordaz@redhat.com>