message: Further simplify character type handling
diff: @@ -1451,9 +1451,12 @@ class input_stream_adapter : public input_adapter_protocol
  input_stream_adapter(const input_stream_adapter&) = delete;
  input_stream_adapter& operator=(input_stream_adapter&) = delete;
  + // std::istream/std::streambuf use std::char_traits<char>::to_int_type, to
  + // ensure that std::char_traits<char>::eof() and the character 0xff do not
  + // end up as the same value, eg. 0xffffffff.
  int get_character() override
  {
  - return reinterpret_cast<int>( sb->sbumpc() );
  + return sb->sbumpc();
  }
  void unget_character() override
  @@ -1489,10 +1492,10 @@ class input_buffer_adapter : public input_adapter_protocol
  {
  if (JSON_LIKELY(cursor < limit))
  {
  - return reinterpret_cast<int>(std::char_traits<char>::to_int_type(*(cursor++)));
  + return std::char_traits<char>::to_int_type(*(cursor++));
  }
  - return reinterpret_cast<int>(std::char_traits<char>::eof());
  + return std::char_traits<char>::eof();
  }
  void unget_character() noexcept override
  