message: hammer: fixed a warning in MSVC
diff: @@ -10323,7 +10323,7 @@ class basic_json
  // refill
  is.read(reinterpret_cast<char*>(buffer.data()), static_cast<std::streamsize>(buffer.size()));
  // set unfilled characters to EOF
  - std::fill_n(buffer.begin() + is.gcount(),
  + std::fill_n(buffer.begin() + static_cast<int>(is.gcount()),
  buffer.size() - static_cast<size_t>(is.gcount()),
  std::char_traits<char>::eof());
  // the buffer is ready
  