Cell size filter dies with CTH AMR

The cell size filter is dying when run on a CTH AMR dataset. Here is how to replicate:

master 5/1/2020 (and 5.8.0), Linux, local server.
Load spcta_a.4.[0-3]. All vars on. Apply. (I believe this is called something like dave's small cth at Kitware).
cell size filter. Unselect everything other than Compute Volume. Apply.

Crash.

This is an important filter for CTH, since it could be used to calculate density.

@cory.quammen Could we possibly move this one to 5.8.1?

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