message: Fix coverity issue#1506497
diff: @@ -242,6 +242,7 @@ static bool swoole_signalfd_create() {
  signal_fd = signalfd(-1, &signalfd_mask, SFD_NONBLOCK | SFD_CLOEXEC);
  if (signal_fd < 0) {
  swoole_sys_warning("signalfd() failed");
  + signal_fd = 0;
  return false;
  }
  signal_socket = swoole::make_socket(signal_fd, SW_FD_SIGNAL);
  @@ -250,6 +251,7 @@ static bool swoole_signalfd_create() {
  signal_socket->fd = -1;
  signal_socket->free();
  close(signal_fd);
  + signal_socket = nullptr;
  signal_fd = 0;
  return false;
  }
  