public void HandleFallback(
            char[] chars, ref int charIndex, ref int charCount,
            byte[] bytes, ref int byteIndex, ref int byteCount, object state)
        {
            EncoderFallbackBuffer buffer = FallbackBuffer;

            encoding.HandleFallback(ref buffer, chars, ref charIndex, ref charCount,
                                    bytes, ref byteIndex, ref byteCount, state);
        }