Order array has to have the same size as item list in wxRearrangeList

Number of indices stored in the internal order array has to be the same as
number of the items, so whenever item is added or removed, order array
has to be adjusted accordingly.

Closes #17836.

include/wx/rearrangectrl.h

@@ -99,6 +99,10 @@ public:
     // Override this to keep our m_order array in sync with the real item state.
     virtual void Check(unsigned int item, bool check = true) wxOVERRIDE;
 
+    int DoInsertOneItem(const wxString& item, unsigned int pos) wxOVERRIDE;
+    void DoDeleteOneItem(unsigned int n) wxOVERRIDE;
+    void DoClear() wxOVERRIDE;
+
 private:
     // swap two items at the given positions in the listbox
     void Swap(int pos1, int pos2);