Return reference on iterator indirection/subscript

modules/core/include/opencv2/core/mat.hpp

@@ -2880,9 +2880,9 @@ public:
     //! copy operator
     MatConstIterator_& operator = (const MatConstIterator_& it);
     //! returns the current matrix element
-    _Tp operator *() const;
+    const _Tp& operator *() const;
     //! returns the i-th matrix element, relative to the current
-    _Tp operator [](ptrdiff_t i) const;
+    const _Tp& operator [](ptrdiff_t i) const;
 
     //! shifts the iterator forward by the specified number of elements
     MatConstIterator_& operator += (ptrdiff_t ofs);

modules/core/include/opencv2/core/mat.inl.hpp

@@ -2550,7 +2550,7 @@ MatConstIterator_<_Tp>& MatConstIterator_<_Tp>::operator = (const MatConstIterat
 }
 
 template<typename _Tp> inline
-_Tp MatConstIterator_<_Tp>::operator *() const
+const _Tp& MatConstIterator_<_Tp>::operator *() const
 {
     return *(_Tp*)(this->ptr);
 }
@@ -2656,7 +2656,7 @@ MatConstIterator_<_Tp> operator - (const MatConstIterator_<_Tp>& a, ptrdiff_t of
 }
 
 template<typename _Tp> inline
-_Tp MatConstIterator_<_Tp>::operator [](ptrdiff_t i) const
+const _Tp& MatConstIterator_<_Tp>::operator [](ptrdiff_t i) const
 {
     return *(_Tp*)MatConstIterator::operator [](i);
 }