vtkSMFieldDataDomain: Fix default_values selection
vtkSMFieldDataDomain::ComputeDefaultValues was faulty in its logic interpreting enum values as indices.
This was working by chance on classic point/cell/field dataset but not working at all with other datasets.
This fixes it by considering the default_values as an enum value, eg vtkDataObject::FIELD or vtkDataObject::POINT as everywhere else in vtkSMFieldDataDomain.