Adapt to 'premature' events being sent from editor controls (fixes datepicker editor crash)

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@55599 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/propgrid/propgrid.cpp

@@ -3307,7 +3307,7 @@ void wxPropertyGrid::OnCustomEditorEvent( wxCommandEvent &event )
         }
     }
 
-    if ( !buttonWasHandled )
+    if ( wnd && !buttonWasHandled )
     {
         // First call editor class' event handler.
         const wxPGEditor* editor = selected->GetEditorClass();