haveNCharacters method
Implementation
@override
bool haveNCharacters(int index, int n) {
  if (index + n - 1 >= bytes.length) {
    return false;
  }
  for (int i = 0; i < n; i++) {
    if (isECI(index + i)) {
      return false;
    }
  }
  return true;
}