CollisionWorld::update hits 'assertion failed: self.pts[2] == id'

Here's the stack:

```
thread '' panicked at 'assertion failed: self.pts[2] == id', /Users/duncan/.cargo/registry/src/github.com-1ecc6299db9ec823/ncollide3d-0.20.1/src/query/algorithms/epa3.rs:143:13
stack backtrace:
0: std::panicking::default_hook::{{closure}}
1: std::panicking::default_hook
2: as core::panic::BoxMeUp>::get
3: std::panicking::begin_panic
4: ncollide3d::query::algorithms::epa3::EPA::compute_silhouette
at /Users/duncan/.cargo/registry/src/github.com-1ecc6299db9ec823/ncollide3d-0.20.1/src/query/algorithms/epa3.rs:0
5: ncollide3d::query::algorithms::epa3::EPA::closest_points
at /Users/duncan/.cargo/registry/src/github.com-1ecc6299db9ec823/ncollide3d-0.20.1/src/query/algorithms/epa3.rs:364
6: ncollide3d::query::contact::contact_support_map_support_map::contact_support_map_support_map_with_params
at /Users/duncan/.cargo/registry/src/github.com-1ecc6299db9ec823/ncollide3d-0.20.1/src/query/contact/contact_support_map_support_map.rs:72
7: as ncollide3d::pipeline::narrow_phase::contact_generator::contact_manifold_generator::ContactManifoldGenerator>::generate_contacts
at /Users/duncan/.cargo/registry/src/github.com-1ecc6299db9ec823/ncollide3d-0.20.1/src/pipeline/narrow_phase/contact_generator/convex_polyhedron_convex_polyhedron_manifold_generator.rs:95
8: ncollide3d::pipeline::narrow_phase::narrow_phase::NarrowPhase::update_contact
at /Users/duncan/.cargo/registry/src/github.com-1ecc6299db9ec823/ncollide3d-0.20.1/src/pipeline/narrow_phase/narrow_phase.rs:73
9: ncollide3d::pipeline::narrow_phase::narrow_phase::NarrowPhase::update_interaction
at /Users/duncan/.cargo/registry/src/github.com-1ecc6299db9ec823/ncollide3d-0.20.1/src/pipeline/narrow_phase/narrow_phase.rs:152
10: ncollide3d::pipeline::narrow_phase::narrow_phase::NarrowPhase::update
at /Users/duncan/.cargo/registry/src/github.com-1ecc6299db9ec823/ncollide3d-0.20.1/src/pipeline/narrow_phase/narrow_phase.rs:180
11: ncollide3d::pipeline::glue::update::perform_narrow_phase
at /Users/duncan/.cargo/registry/src/github.com-1ecc6299db9ec823/ncollide3d-0.20.1/src/pipeline/glue/update.rs:93
12: ncollide3d::pipeline::glue::update::perform_all_pipeline
at /Users/duncan/.cargo/registry/src/github.com-1ecc6299db9ec823/ncollide3d-0.20.1/src/pipeline/glue/update.rs:109
13: ncollide3d::pipeline::world::CollisionWorld::update
at /Users/duncan/.cargo/registry/src/github.com-1ecc6299db9ec823/ncollide3d-0.20.1/src/pipeline/world.rs:105
```

I'm not really sure what leads to this. All I know is that it happens more often with large density of cuboids in my world.

My code is generating a bunch of random (integer size and location) axis-aligned cuboids inside some 3D region.

EDIT: Just see the code in my next comment.