Don't label data outside of dataset bbox

[philippotto]

Labeling volume data outside of the dataset's bbox does not produce visible labels in the viewports. However, ad-hoc meshing the segment shows that data is stored outside of the dataset's bbox. Ideally, this data should not be produced so that other code (such as meshing or download) does not handle this data which the user has never seen before.

[philippotto]

I think, buckets which are completely outside of the DS bbox are not created, anyway. However, buckets which overlap are probably created and bbox checks would need to be introduce dwhen labeling these.