fix a segfault
fix a segfault

hemingcui/libevent_paxos,milannic/libevent_paxos,milannic/libevent_paxos,hemingcui/libevent_paxos,hemingcui/libevent_paxos,hemingcui/libevent_paxos,milannic/libevent_paxos,milannic/libevent_paxos,hemingcui/libevent_paxos,milannic/libevent_paxos,hemingcui/libevent_paxos,hemingcui/libevent_paxos,milannic/libevent_paxos,hemingcui/libevent_paxos,milannic/libevent_paxos,milannic/libevent_paxos