message: Change ofstream fail() to operator()
  This one I've missed in the last commit doing that.
diff: @@ -222,7 +222,7 @@ private:
  inline void save_rendering_parameters(RenderingParameters rendering_parameters, std::string filename)
  {
  std::ofstream file(filename);
  - if (file.fail())
  + if (!file)
  {
  throw std::runtime_error("Error opening file for writing: " + filename);
  }
  