message: Document recent patch to the Qt group chat example
diff: @@ -15,6 +15,7 @@ is based on [Keep a Changelog](https://keepachangelog.com).
  the closing parenthesis.
  - The JSON reader now automatically widens integers to doubles as necessary.
  - Module options (e.g. for the `middleman`) now show up in `--long-help` output.
  +- Fix undefined behavior in the Qt group chat example (#1336).
  ### Changed
  