Padding calculation wrong when starting position % 4 != 0

[5andr0]

private void SkipPadding()
    {
        var bytes = (int)(BaseStream.Position % 4);

I have a BaseStream where the xz file doesn't start at position 0. If this position is not dividable by 4, then the padding calculation is wrong.
Please fix this by calculating the position from the starting position. Thanks