message: throw if no id is set for the model
diff: @@ -48,6 +48,9 @@ namespace ospray {
  {
  Model::commit();
  id = getParam1i("id", -1);
  + if (id == -1) {
  + throw std::runtime_error("#osp:error An id must be set for the model");
  + }
  // TODO: We should take an optional clipping box to shrink the
  // model's bounds, for example if we want to clip some sphere
  // or other geometry to be smaller and contained within the actual
  