OpenVDB will throw an exception when trying to prune a SDF/Level-Set grid with a
negative background value.
The geometry nodes in this case are constructing a nominal SDF grid from a
generic "density" volume cube. The negative background value results from
processing the background value the same way as all other grid values in the new
field+grid math feature (`blender::nodes::process_background`).
Since any grid can be constructed with a negative background value we have to
check and correct this before calling the OpenVDB prune function.
Pull Request: https://projects.blender.org/blender/blender/pulls/146837
9aade6bd61