correctly handle default domain id

[trittsv]

<CycloneDDS>
  <Domain id="33">
     ...
  </Domain>
</CycloneDDS>

and if you then call use domain id DDS_DOMAIN_DEFAULT (=2**32-1=dds_domain_default in python) in dds_create_participant it uses 33 because that's the first id it can find anywhere.