message: Fix crash on exit in opencv_annotation
  destroyWindow was called twice during completion of the
  annotation procedure, resulting in a crash, and failure to write
  an output file
diff: @@ -140,7 +140,6 @@ vector<Rect> get_annotations(Mat input_image)
  switch( key_pressed )
  {
  case 27:
  - destroyWindow(window_name);
  stop = true;
  break;
  case 99:
  