imgproc(segmentation): don't increase mask NULL pointer

Avoid manual address arithmetic

modules/imgproc/src/segmentation.cpp

@@ -407,27 +407,25 @@ void cv::pyrMeanShiftFiltering( InputArray _src, OutputArray _dst,
         cv::Size size = src.size();
         const uchar* sptr = src.ptr();
         int sstep = (int)src.step;
-        uchar* mask = 0;
-        int mstep = 0;
         uchar* dptr;
         int dstep;
         float sp = (float)(sp0 / (1 << level));
         sp = MAX( sp, 1 );
 
+        cv::Mat m;
         if( level < max_level )
         {
             cv::Size size1 = dst_pyramid[level+1].size();
-            cv::Mat m( size.height, size.width, CV_8UC1, mask0.ptr() );
+            m = cv::Mat(size.height, size.width, CV_8UC1, mask0.ptr());
             dstep = (int)dst_pyramid[level+1].step;
             dptr = dst_pyramid[level+1].ptr() + dstep + cn;
-            mstep = (int)m.step;
-            mask = m.ptr() + mstep;
             //cvResize( dst_pyramid[level+1], dst_pyramid[level], CV_INTER_CUBIC );
             cv::pyrUp( dst_pyramid[level+1], dst_pyramid[level], dst_pyramid[level].size() );
             m.setTo(cv::Scalar::all(0));
 
-            for( i = 1; i < size1.height-1; i++, dptr += dstep - (size1.width-2)*3, mask += mstep*2 )
+            for( i = 1; i < size1.height-1; i++, dptr += dstep - (size1.width-2)*3)
             {
+                uchar* mask = m.ptr(1 + i * 2);
                 for( j = 1; j < size1.width-1; j++, dptr += cn )
                 {
                     int c0 = dptr[0], c1 = dptr[1], c2 = dptr[2];
@@ -437,16 +435,16 @@ void cv::pyrMeanShiftFiltering( InputArray _src, OutputArray _dst,
             }
 
             cv::dilate( m, m, cv::Mat() );
-            mask = m.ptr();
         }
 
         dptr = dst_pyramid[level].ptr();
         dstep = (int)dst_pyramid[level].step;
 
         for( i = 0; i < size.height; i++, sptr += sstep - size.width*3,
-                                          dptr += dstep - size.width*3,
-                                          mask += mstep )
+                                          dptr += dstep - size.width*3
+        )
         {
+            uchar* mask = m.empty() ? NULL : m.ptr(i);
             for( j = 0; j < size.width; j++, sptr += 3, dptr += 3 )
             {
                 int x0 = j, y0 = i, x1, y1, iter;