Fix calling wxFileHistory::Load() more than once.

Don't add all the items in the history to the menu again, remove the old ones
if we had already added them.

Closes #16588.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@78013 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/filehistory.h

@@ -78,6 +78,9 @@ private:
     // this to ensure the same normalization is used everywhere.
     static wxString NormalizeFileName(const wxFileName& filename);
 
+    // Remove any existing entries from the associated menus.
+    void RemoveExistingHistory();
+
     wxDECLARE_NO_COPY_CLASS(wxFileHistoryBase);
 };