compilation fix after NULL cast removal; also used it to get rid of an ugly OnTimerEvent(*(wxTimerEvent *)NULL) call

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@58229 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/msw/combo.h

@@ -73,10 +73,13 @@ public:
     static int GetFeatures() { return wxComboCtrlFeatures::All; }
 
 #if wxUSE_COMBOCTRL_POPUP_ANIMATION
-    void OnTimerEvent( wxTimerEvent& event );
+    void OnTimerEvent(wxTimerEvent& WXUNUSED(event)) { DoTimerEvent(); }
+
 protected:
+    void DoTimerEvent();
+
     virtual bool AnimateShow( const wxRect& rect, int flags );
-#endif
+#endif // wxUSE_COMBOCTRL_POPUP_ANIMATION
 
 protected: