message: remove a useless statement.
diff: @@ -513,10 +513,6 @@ bool findChessboardCorners(InputArray image_, Size pattern_size,
  {
  cvtColor(img, img, COLOR_BGR2GRAY);
  }
  - else
  - {
  - img.clone();
  - }
  int prev_sqr_size = 0;
  @@ -578,6 +574,7 @@ bool findChessboardCorners(InputArray image_, Size pattern_size,
  {
  if (flags & CALIB_CB_NORMALIZE_IMAGE)
  {
  + img = img.clone();
  equalizeHist(img, img);
  }
  