message: set path curve material to thin glass
  so it's see-through if showing path is enabled while camera is still on
  the path
diff: @@ -1707,13 +1707,17 @@ void MainWindow::buildWindowKeyframes()
  std::vector<vec4f> colors(vertexes);
  std::fill(colors.begin(), colors.end(), vec4f(vec3f(0.8f), 1.f));
  + const std::vector<uint32_t> mID = {
  + static_cast<uint32_t>(baseMaterialRegistry->children().size())};
  + auto mat = sg::createNode("pathGlass", "thinGlass");
  + baseMaterialRegistry->add(mat);
  +
  path->remove("radius");
  path->createChildData("vertex.position_radius", vertexes);
  path->createChildData("vertex.color", colors);
  path->createChildData("index", indexes);
  path->createChild("type", "uchar", (unsigned char)OSP_ROUND);
  path->createChild("basis", "uchar", (unsigned char)OSP_LINEAR);
  - const std::vector<uint32_t> mID = {0};
  path->createChildData("material", mID);
  path->child("material").setSGOnly();
  