cell_iterator - operator* const overloads

Users may still want to derederence a const iterator (note: not a const_iterator).
Also use the "reference" typedef to ensure there is only 1 source of information

include/xlnt/worksheet/cell_iterator.hpp

@@ -89,7 +89,13 @@ public:
     /// <summary>
     /// Dereferences this iterator to return the cell it points to.
     /// </summary>
-    cell operator*();
+    reference operator*();
+
+    /// <summary>
+    /// Dereferences this iterator to return the cell it points to.
+    /// </summary>
+    const reference operator*() const;
+
 
     /// <summary>
     /// Returns true if this iterator is equivalent to other.
@@ -207,6 +213,12 @@ public:
     /// destructor for const_cell_iterator
     /// </summary>
     ~const_cell_iterator() = default;
+
+    /// <summary>
+    /// Dereferences this iterator to return the cell it points to.
+    /// </summary>
+    const reference operator*() const;
+
     /// <summary>
     /// Dereferences this iterator to return the cell it points to.
     /// </summary>

source/worksheet/cell_iterator.cpp

@@ -265,14 +265,18 @@ const_cell_iterator const_cell_iterator::operator++(int)
     return old;
 }
 
-cell cell_iterator::operator*()
+cell_iterator::reference cell_iterator::operator*()
 {
     return ws_.cell(cursor_);
 }
 
-const cell const_cell_iterator::operator*() const
+const cell_iterator::reference cell_iterator::operator*() const
 {
     return ws_.cell(cursor_);
 }
 
+const const_cell_iterator::reference const_cell_iterator::operator*() const
+{
+    return ws_.cell(cursor_);
+}
 } // namespace xlnt