message: fix the bug: wrong TID dose not unlock table_lock
diff: @@ -49,6 +49,7 @@ shared_ptr<Transaction> Txn_manager::get_transaction(txn_id_t TID)
  {
  table_lock.lockShared();
  if(txn_table.find(TID) == txn_table.end()) {
  + table_lock.unlock();
  cerr << "wrong TID" << endl;
  return nullptr;
  }
  