message: Resolve OSPRay warning on glTF HDRI filename.
  By recreating the child "filename" it was no longer marked as setSGOnly,
  so OSPRay warned when receiving the parameter.
diff: @@ -234,7 +234,7 @@ void GLTFData::applySceneBackground(NodePtr bgXfm)
  auto &bgFileName = background.Get("background-uri").Get<std::string>();
  rkcommon::FileName bgTexture = fileName.path() + bgFileName;
  auto bgNode = createNode("background", "hdri");
  - bgNode->createChild("filename", "filename", bgTexture.str());
  + bgNode->child("filename") = bgTexture.str();
  if (background.Has("rotation")) {
  const auto &r = background.Get("rotation").Get<tinygltf::Value::Array>();
  