fcgi/Client: hold pool reference while invoking HttpResponseHandler
fcgi/Client: hold pool reference while invoking HttpResponseHandler

Fix possible regression from commit
47274422a6dbc8459817f0785f7fb055ed18bb42

CM4all/beng-proxy,CM4all/beng-proxy,CM4all/beng-proxy,CM4all/beng-proxy,CM4all/beng-proxy,CM4all/beng-proxy