Merge pull request #6236 from alalek:backport_6232

modules/core/src/matrix.cpp

@@ -3439,7 +3439,7 @@ ptrdiff_t operator - (const MatConstIterator& b, const MatConstIterator& a)
     if( a.m != b.m )
         return INT_MAX;
     if( a.sliceEnd == b.sliceEnd )
-        return (b.ptr - a.ptr)/b.elemSize;
+        return (b.ptr - a.ptr)/static_cast<ptrdiff_t>(b.elemSize);
 
     return b.lpos() - a.lpos();
 }