Fixed: #1301 A temporary fix instead of the future of undo command delete landscape.

--HG--
branch : gsoc2011-worldeditorqt

code/nel/tools/3d/object_viewer_qt/src/plugins/landscape_editor/landscape_editor_window.cpp

@@ -245,6 +245,8 @@ void LandscapeEditorWindow::deleteSelectedLand()
 
 	if (m_ui.landscapesListWidget->count() == 1)
 		m_ui.deleteLandAction->setEnabled(false);
+
+	m_undoStack->clear();
 }
 
 int LandscapeEditorWindow::createLandscape(const QString &fileName)