message: Fix utf8_to_wstring error on Windows
diff: #include <locale>
  #endif
  -
  using namespace realm;
  namespace {
  @@ -49,8 +48,15 @@ std::wstring utf8_to_wstring(StringData str)
  #if defined(_MSC_VER)
  // __STDC_UTF_16__ seems not to work
  static_assert(sizeof(wchar_t) == 2, "Expected Windows to use utf16");
  - std::wstring_convert<std::codecvt_utf8_utf16<wchar_t>> utf8conv;
  - auto w_result = utf8conv.from_bytes(str.data(), str.data() + str.size());
  +
  + // First get the number of chars needed for output buffer
  + int wchars_num = MultiByteToWideChar(CP_UTF8, 0, str.data(), -1, nullptr, 0);
  + wchar_t* wstr = new wchar_t[wchars_num];
  + // Then convert
  + MultiByteToWideChar(CP_UTF8, 0, str.data(), -1, wstr, wchars_num);
  + std::wstring w_result{wstr};
  + delete[] wstr;
  +
  return w_result;
  #else
  // gcc 4.7 and 4.8 do not yet support codecvt_utf8_utf16 and wstring_convert, and note that we can NOT just use
  