rcc has crash bug in the framework now

[shuaimu]

happens /home/shuai/bworkspace/baroque/deptran/rcc/dep_graph.cc:55

uint64_t DepGraph::sub_txn_graph(
        uint64_t tid,
        GraphMarshaler &gra_m
) {
    gra_m.gra = &txn_gra_;

    Vertex *source = txn_gra_.FindV(tid);

    verify(source != NULL);

    // Log::debug("compute for sub graph, tid: %llx parent size: %d",
    //     tid, (int) source->from_.size());

    auto &ret_set = gra_m.ret_set;

    find_txn_anc_opt(source, ret_set);
    ret_set.insert(source);
    return ret_set.size();
}