Stomp on memory in dialog dtors to detect bugs

git-svn-id: svn+ssh://svn.code.sf.net/p/supertuxkart/code/main/trunk@6365 178a84e3-b1eb-0310-8ba1-8eac791a3b58

src/guiengine/modaldialog.cpp

@@ -122,6 +122,7 @@ ModalDialog::~ModalDialog()
     GUIEngine::getGUIEnv()->removeFocus( m_irrlicht_window );
     
     m_irrlicht_window->remove();
+    m_irrlicht_window = NULL;
     
     if (modalWindow == this) modalWindow = NULL;
     

src/states_screens/dialogs/confirm_dialog.hpp

@@ -59,6 +59,8 @@ public:
       */
     ConfirmDialog(irr::core::stringw msg, IConfirmDialogListener* listener);
     
+    ~ConfirmDialog() { m_listener = NULL; }
+    
     virtual void onEnterPressedInternal();
     
     GUIEngine::EventPropagation processEvent(const std::string& eventSource);