message: overdrawanalyzer: Report overdraw=0 for empty meshes
  Before this change empty meshes would result in overdraw=NaN since no
  pixels would be rendered.
diff: @@ -216,7 +216,7 @@ namespace
  delete buffer;
  - result.overdraw = static_cast<float>(result.pixels_shaded) / static_cast<float>(result.pixels_covered);
  + result.overdraw = result.pixels_covered ? float(result.pixels_shaded) / float(result.pixels_covered) : 0.f;
  return result;
  }
  