xatlas: fix crash caused by faulty spatial hash.
xatlas: fix crash caused by faulty spatial hash.

If A and B are equal keys, then hash(A) and hash(B) should be equal, but
xatlas was violating this constraint.

This bug was not present in Thekla's original code, it was introduced
later by the xatlas project.

google/filament,google/filament,google/filament,google/filament,google/filament,google/filament,google/filament,google/filament,google/filament,google/filament,google/filament,google/filament