handle huge matrices correctly (#11505)

* make sure that the matrix with more than INT_MAX elements is marked as non-continuous, and thus all the pixel-wise functions process it correctly (i.e. row-by-row, not as a single row, where integer overflow may occur when computing the total number of elements)

modules/core/src/matrix_c.cpp

@@ -120,8 +120,8 @@ static Mat iplImageToMat(const IplImage* img, bool copyData)
     }
     m.datalimit = m.datastart + m.step.p[0]*m.rows;
     m.dataend = m.datastart + m.step.p[0]*(m.rows-1) + esz*m.cols;
-    m.flags |= (m.cols*esz == m.step.p[0] || m.rows == 1 ? Mat::CONTINUOUS_FLAG : 0);
     m.step[1] = esz;
+    m.updateContinuityFlag();
 
     if( copyData )
     {