Fix crash when appending menuitem after removing it from another menu.

Also remove unused return value from GtkAppend

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@69878 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/gtk/menu.h

@@ -51,7 +51,7 @@ public:
 
 private:
     // common part of Append and Insert
-    bool GtkAppend(wxMenu *menu, const wxString& title, int pos=-1);
+    void GtkAppend(wxMenu* menu, const wxString& title, int pos = -1);
 
     void Init(size_t n, wxMenu *menus[], const wxString titles[], long style);
 
@@ -99,7 +99,7 @@ private:
     void Init();
 
     // common part of Append (if pos == -1)  and Insert
-    bool GtkAppend(wxMenuItem *item, int pos=-1);
+    void GtkAppend(wxMenuItem* item, int pos = -1);
 
 
     DECLARE_DYNAMIC_CLASS(wxMenu)