added conversion ctor to create const_iterator from iterator, otherwise assigning the return value of begin() called on a non-const object to a const_iteator didn't work

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@39112 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/hashmap.h

@@ -202,6 +202,7 @@ public: \
     { \
     public: \
         const_iterator() : Iterator() {} \
+        const_iterator(iterator i) : Iterator(i) {} \
         const_iterator( Node* node, const Self* ht ) \
             : Iterator( node, (Self*)ht ) {} \
         const_iterator& operator++() { PlusPlus();return *this; } \