message: Check the result of wait_merging_threads
diff: @@ -208,7 +208,7 @@ fn run_example(index_path: &Path) -> tantivy::Result<()> {
  // Usually this isn't needed, but in `main` we try to
  // delete the temporary directory and that fails on
  // Windows if the files are still open.
  - index_writer.wait_merging_threads();
  + index_writer.wait_merging_threads()?;
  Ok(())
  }
  