message: fix bug where node validity check wasn't properly changing back text color
diff: @@ -288,7 +288,8 @@ namespace ospray {
  void guiSGTree(const std::string &name, std::shared_ptr<sg::Node> node)
  {
  int styles = 0;
  - if (!node->isValid()) {
  + bool nodeValid = node->isValid();
  + if (!nodeValid) {
  ImGui::PushStyleColor(ImGuiCol_Text, ImVec4(0.8f, 0.06f, 0.02f, 1.f));
  styles++;
  }
  @@ -305,7 +306,7 @@ namespace ospray {
  guiSGSingleNode(text, node);
  - if (!node->isValid())
  + if (!nodeValid)
  ImGui::PopStyleColor(styles--);
  if (node->hasChildren()) {
  