/* we can only join tracks if there was a last tp, the last tp was an endpoint, _AND_ this tp is an endpoint */
SET_BUTTON_SENSITIVE ( tpwin, VIK_TRW_LAYER_TPWIN_JOIN, tpwin->cur_tp && tpwin->cur_tp_is_endpoint && (!(tpl->next && tpl->prev)) );
/* we can only join tracks if there was a last tp, the last tp was an endpoint, _AND_ this tp is an endpoint */
SET_BUTTON_SENSITIVE ( tpwin, VIK_TRW_LAYER_TPWIN_JOIN, tpwin->cur_tp && tpwin->cur_tp_is_endpoint && (!(tpl->next && tpl->prev)) );