Avoid segfault on a case where the server somehow replies before we send anything like a request.
Avoid segfault on a case where the server somehow replies before we send
anything like a request.

Reproducable by:
$ nc -Sl 127.0.0.1 9001 < response.txt
$ serf_get http://127.0.0.1:9001/

Where serf_get is somehow slow (e.g. when debugging)

* outgoing.c
  (read_from_connection): Before accepting a response make sure there
    is somebody willing to accept it, or we have a segfault.

jandre/serf,jandre/serf,jandre/serf,jandre/serf