message: fix num_vals in multivalue index after merge
diff: @@ -126,6 +126,8 @@ impl<'a> RemappedDocIdMultiValueIndexColumn<'a> {
  num_vals += segment_reader.num_docs();
  multi_value_length_readers.push(multi_value_length_reader);
  }
  + // The value range is always get_val(doc)..get_val(doc + 1)
  + num_vals += 1;
  Self {
  doc_id_mapping,
  multi_value_length_readers,
  