message: Refactor utf8_validate() to avoid dead stores
diff: @@ -53,16 +53,17 @@ bool utf8_validate(const uint8_t* pos, const uint8_t* end) noexcept
  {
  while (pos < end)
  {
  - int required_bytes = 1;
  - auto byte2_rule = Rule::Range80BF;
  -
  const uint8_t byte1 = *pos++;
  if (byte1 <= 0x7F)
  - // Shortcut for valid ASCII (also valid UTF-8)
  - continue;
  - else if (byte1 < 0xC2)
  - return false; // NOLINT(bugprone-branch-clone)
  - else if (byte1 <= 0xDF)
  + continue; // Shortcut for valid ASCII (also valid UTF-8)
  +
  + if (byte1 < 0xC2)
  + return false;
  +
  + // Discover requirements.
  + int required_bytes;
  + Rule byte2_rule;
  + if (byte1 <= 0xDF)
  {
  required_bytes = 2;
  byte2_rule = Rule::Range80BF;
  