Fixed one crash with battle mode (though it still doesn't work fully).

git-svn-id: svn+ssh://svn.code.sf.net/p/supertuxkart/code/main/trunk@6312 178a84e3-b1eb-0310-8ba1-8eac791a3b58

src/tracks/track.cpp

@@ -742,6 +742,7 @@ void Track::loadTrackModel(World* parent, unsigned int mode_id)
         default_start->get("karts-per-row",      &karts_per_row     );
     }
     m_start_transforms.resize(race_manager->getNumberOfKarts());
+    if(!m_is_arena)
         m_quad_graph->setDefaultStartPositions(&m_start_transforms,
                                                karts_per_row,
                                                forwards_distance,