message: Fix streaming of variants
diff: @@ -82,15 +82,15 @@ public:
  using type = detail::decay_t<decltype(*i)>;
  // Ship full batches.
  while (std::distance(i, e) >= desired_batch_size) {
  - std::vector<type> tmp{std::make_move_iterator(i),
  - std::make_move_iterator(i + desired_batch_size)};
  + std::vector<type> tmp(std::make_move_iterator(i),
  + std::make_move_iterator(i + desired_batch_size));
  emit_batch(self, desired_batch_size, make_message(std::move(tmp)));
  i += desired_batch_size;
  }
  // Ship underful batch only if `force_underful` is set.
  if (i != e && force_underfull) {
  - std::vector<type> tmp{std::make_move_iterator(i),
  - std::make_move_iterator(e)};
  + std::vector<type> tmp(std::make_move_iterator(i),
  + std::make_move_iterator(e));
  auto tmp_size = static_cast<int32_t>(tmp.size());
  emit_batch(self, tmp_size, make_message(std::move(tmp)));
  return e;
  