Add an extra assert in the case of trying to load an invalid history item

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/branches/SOC2011_WEBVIEW@68118 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/msw/webview_ie.cpp

@@ -381,6 +381,7 @@ void wxWebViewIE::LoadHistoryItem(wxWebHistoryItem* item)
         if(m_historyList[i].get() == item)
             pos = i;
     }
+    wxASSERT_MSG(pos != m_historyList.size(), "invalid history item");
     m_historyLoadingFromList = true;
     LoadUrl(item->GetUrl());
     m_historyPosition = pos;