message: Do not reset step for single-row Mat created on user data
diff: @@ -508,7 +508,6 @@ Mat::Mat(int _rows, int _cols, int _type, void* _data, size_t _step)
  }
  else
  {
  - if( rows == 1 ) _step = minstep;
  CV_DbgAssert( _step >= minstep );
  if (_step % esz1 != 0)
  @@ -516,7 +515,8 @@ Mat::Mat(int _rows, int _cols, int _type, void* _data, size_t _step)
  CV_Error(Error::BadStep, "Step must be a multiple of esz1");
  }
  - flags |= _step == minstep ? CONTINUOUS_FLAG : 0;
  + if (_step == minstep || rows == 1)
  + flags |= CONTINUOUS_FLAG;
  }
  step[0] = _step;
  step[1] = esz;
  @@ -541,7 +541,6 @@ Mat::Mat(Size _sz, int _type, void* _data, size_t _step)
  }
  else
  {
  - if( rows == 1 ) _step = minstep;
  CV_DbgAssert( _step >= minstep );
  if (_step % esz1 != 0)
  @@ -549,7 +548,8 @@ Mat::Mat(Size _sz, int _type, void* _data, size_t _step)
  CV_Error(Error::BadStep, "Step must be a multiple of esz1");
  }
  - flags |= _step == minstep ? CONTINUOUS_FLAG : 0;
  + if (_step == minstep || rows == 1)
  + flags |= CONTINUOUS_FLAG;
  }
  step[0] = _step;
  step[1] = esz;
  