v.external: fix bug: open on level 1 before building topology

git-svn-id: https://svn.osgeo.org/grass/grass/trunk@51971 15284696-431f-4ddb-bdfa-cd5b030d7da7

vector/v.external/main.c

@@ -187,6 +187,7 @@ int main(int argc, char *argv[])
     fclose(fd);
     
     if (!flags.topo->answer) {
+        Vect_set_open_level(1);
         Vect_open_old(&Map, output, G_mapset());
         Vect_build(&Map);
         Vect_close(&Map);