fixed MatConstIterator::operator *()   (the bug caused "operations" test failure; ticket #613)
fixed MatConstIterator::operator *()   (the bug caused "operations" test failure; ticket #613)

opencv/opencv,apavlenko/opencv,apavlenko/opencv,opencv/opencv,apavlenko/opencv,opencv/opencv,opencv/opencv,opencv/opencv,apavlenko/opencv,opencv/opencv,opencv/opencv,opencv/opencv,opencv/opencv,apavlenko/opencv,apavlenko/opencv,opencv/opencv