don't assert if 'c' key is pressed when there is no selection

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@43379 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

samples/listctrl/listtest.cpp

@@ -915,6 +915,12 @@ void MyListCtrl::OnListKeyDown(wxListEvent& event)
             {
                 wxListItem info;
                 info.m_itemId = event.GetIndex();
+                if ( info.m_itemId == -1 )
+                {
+                    // no item
+                    break;
+                }
+
                 GetItem(info);
 
                 wxListItemAttr *attr = info.GetAttributes();