message: Fix sign-compare warning on GCC
diff: @@ -49,7 +49,8 @@ bool load_data(Deserializer& source, message::data_ptr& data) {
  GUARDED(source.begin_field("types"));
  size_t msg_size = 0;
  GUARDED(source.begin_sequence(msg_size));
  - if (msg_size > std::numeric_limits<uint16_t>::max() - 1)
  + using uint16_limits = std::numeric_limits<uint16_t>;
  + if (msg_size > static_cast<size_t>(uint16_limits::max() - 1))
  STOP(sec::invalid_argument, "too many types for message");
  if (msg_size == 0) {
  data.reset();
  