Bounding Boxes don't align with actual volumes

[smlpt]

Tested with a simple BDV XML:

This is likely caused by the changes that fixed the volume scaling to properly display anisotropic volumes, but the bounding grid code wasn't updated accordingly.

(backlink to the discussion)

[smlpt]

So far I could only observe the behavior with buffered volumes, aka xml-based ones, and not with TIF files. I think TIFs are not compensated for the anisotropic scaling, so the issue does not appear there.