A data race missing acquring locks

[ryancaicse]

There are some inconsistent places about locking clinet_fd

Aaccessing client_fd without locking
https://github.com/bgamari/ghc-eventlog-socket/blob/6c45d6f9e2014114b1125328ed9ea901598d8f7f/eventlog_socket.c#L129-L132

Accessing client_fd with locking
https://github.com/bgamari/ghc-eventlog-socket/blob/6c45d6f9e2014114b1125328ed9ea901598d8f7f/eventlog_socket.c#L42-L45

https://github.com/bgamari/ghc-eventlog-socket/blob/6c45d6f9e2014114b1125328ed9ea901598d8f7f/eventlog_socket.c#L74-L79

[ryancaicse]

@bgamari Hi, can you take a look? Thanks.