message: Fix race condition in send_pong where it races with previous disconnections
diff: @@ -246,9 +246,13 @@ impl Outbound {
  pub(crate) fn send_pong(&self) -> io::Result<()> {
  self.with_writer(|writer| {
  + if !writer.is_disconnected() {
  writer.write_all(b"PONG\r\n")?;
  // Flush in place on pings.
  writer.flush()
  + } else {
  + Ok(())
  + }
  })
  }
  