There was a bug with Flying Edges checking the boundary conditions in
the z-direction. It was comparing the z index to the size of the y
dimension, not the z dimension. This simple typo was probably missed
because most of the tests use square meshes. To catch the problem, you
need a mesh that has a different number of points in the y and z
directions and the contour has to go past the positive z boundary.
When this error was hit, the indices for the edges on that boundary were
not recorded, and later interpolation used garbage values for edge's
point ids.
When the Marching Cubes algorithm merges points together for multiple
isosurfaces, it uses an ArrayHandleZip to combine the isosurface id and
the edge identification. This is to prevent merging points from
different isosurfaces. However, internally this has to do an array copy.
It was doing this copy with `ArrayCopy`. A recent change to that method
made the copy fail for `ArrayHandleZip`. The fix is to change to
`ArrayCopyDevice`.
The reason why this bug was introduced was because there was no test
case for this specific use. A regression test has been updated to test
for this case.
