handle manual res when not returning

[ggurkal]

When we have something like this:

class User {
  users(@Req() req, @Res() res) {
    res.status(200).json({ ok: true });
  }
}

returnValue in the handler waits for a return but it's not coming. So now we check if the headers are already sent to prevent that hanging.

[github-actions]

🎉 This PR is included in version 1.1.3 🎉

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