Minor fixes for sss_parse_name_for_domains
    
    - use brackets after an if
    - use the right variable name (candidate_domain instead of
      candidate_name).
    - fix a typo in a debug message
    - only print a debug message about using a default domain when using a
      default domain
    - add a comment explaning when is a codepath executed
    
    Reviewed-by: Pavel Březina <pbrezina@redhat.com>