message: Build error.  Mismatch between rkcommon::Filename and std::string
  Interestingly, gcc 9.3 on Ubuntu 20.04 didn't even warn.
diff: @@ -26,8 +26,9 @@ namespace ospray {
  const bool preferLinear = false,
  const bool nearestFilter = false);
  + std::string fileName;
  +
  //! texture size, in pixels
  - FileName fileName;
  vec2i size{-1};
  int channels{0};
  int depth{0};
  