Fix a null exception throw if bytes variable is empty

[Lanz86]

When passing a void stream the bytes variable assumes a null value.
After this check
if (bytesRead != (int)args.ObjectSize)
the relative exception

throw new UnexpectedShortReadException(
                    $"Data read {bytes.Length} is shorter than the size {args.ObjectSize} of input buffer.");

throw another exception (NullReference) because bytes variable is null.