`ContactPairView::collider2` can panic when using `in_fixed_schedule`

Hi I recently switched my app to using `in_fixed_schedule` and sometimes (generally when entities are being deleted) `ContactPairView::collider2` panics on unwrapping a `None` value.

For context, I'm trying to get the collider of a contact from `RapierContext::contacts_with` and this is happening in a system which is not in the fixed schedule.

I had never seen this behaviour before switching to `in_fixed_schedule` and it's happening all the time now so I'm very confident the change has something to do with that.

If you like I can try to produce a minimal example of this.