update socket.lua to check if connected

[lurenx]

    connected,connecting = logger.isconnected()
    if  type(connected) ~= "nil" and type(connecting) ~= "nil"  then
        if not connected then
            create_error_response(1000,"server error")
        end
    end
    local bytes, err = logger.log(send_str)
    if err then
        ngx.log(ngx.ERR, "failed to log message: ", err)
        create_error_response(1000,"server error")
    end
    return

we can check the type and value of connected,connecting to response the client different http code if we dont want to lost log.