message: Use correct int type in validation
diff: @@ -53,7 +53,7 @@ bool utf8_validate(const uint8_t* pos, const uint8_t* end) noexcept
  {
  while (pos < end)
  {
  - unsigned required_bytes = 1;
  + int required_bytes = 1;
  auto byte2_rule = Rule::Range80BF;
  const uint8_t byte1 = *pos++;
  @@ -108,7 +108,7 @@ bool utf8_validate(const uint8_t* pos, const uint8_t* end) noexcept
  // At this point need to read at least one more byte.
  assert(required_bytes > 1);
  - if ((end - pos) < required_bytes - 1)
  + if ((end - pos) < (required_bytes - 1))
  return false;
  