drouting: Tolerate a NULL dr_rules.gwlist

In build_rt_info(), there is a NULL check anyway:

    if ( dstlst && dstlst[0]!=0 ) {

... so this patch can only do good, by making the code compatible with
even more flavours of the `dr_rules` table.

modules/drouting/dr_load.c

@@ -627,7 +627,7 @@ rt_data_t* dr_load_routing_info(struct head_db *current_partition,
 			/* ROUTE_ID column */
 			check_val( routeid_drr_col, ROW_VALUES(row)+5, DB_STRING, 0, 0);
 			/* DSTLIST column */
-			check_val( dstlist_drr_col, ROW_VALUES(row)+6, DB_STRING, 1, 1);
+			check_val( dstlist_drr_col, ROW_VALUES(row)+6, DB_STRING, 0, 1);
 			str_vals[STR_VALS_DSTLIST_DRR_COL] =
 				(char*)VAL_STRING(ROW_VALUES(row)+6);
 			/* SORT_ALG column */