message: Simplify using unwrap_or_else
diff: @@ -869,16 +869,12 @@ impl<'cfg> DrainState<'cfg> {
  impl Drop for FinishOnDrop<'_> {
  fn drop(&mut self) {
  - if let Some(result) = self.result.take() {
  + let result = self
  + .result
  + .take()
  + .unwrap_or_else(|| Err(format_err!("worker panicked")));
  self.messages
  .push(Message::Finish(self.id, Artifact::All, result));
  - } else {
  - self.messages.push(Message::Finish(
  - self.id,
  - Artifact::All,
  - Err(format_err!("worker panicked")),
  - ));
  - }
  }
  }
  };
  