Fix minor file descriptor leak
Fix minor file descriptor leak

On server shutdown, the pid file descriptor would be leaked. It wasn't
really a problem, however, since the process would be exiting anyway.

Found with Coverity, CID 88507.

TigerZhang/logcabin,gaoning777/logcabin,logcabin/logcabin,chaozh/logcabin,logcabin/logcabin,logcabin/logcabin,chaozh/logcabin,gaoning777/logcabin,gaoning777/logcabin,chaozh/logcabin,dankenigsberg/logcabin,dankenigsberg/logcabin,dankenigsberg/logcabin,chaozh/logcabin,tempbottle/logcabin,tempbottle/logcabin,tempbottle/logcabin,gaoning777/logcabin,TigerZhang/logcabin,TigerZhang/logcabin,logcabin/logcabin,tempbottle/logcabin,dankenigsberg/logcabin,TigerZhang/logcabin