h2d.filter.Mask in h2d.Bitmat leads to mask being offset

[zommerfelds]

When using new Mask(obj, true), the masked part is not the same as the actually rendered mask.

I have a repo with the repro: https://zommerfelds.github.io/heaps-mask-bug/ (source)

First I thought that the problem was with the mask, but now I'm starting to see that it only happens when the Tile has a dx/dy (set with setCenterRatio) and the Bitmap has a modified width. There is some weird edge case here and the Bitmap is not behaving like I expect.

Don't know if this is related to #201. I think it might rather be something in the Bitmap?