Zombie nautiluses don't have their own saddle equipment entry

Unlike other undead mounts, including the newly added camel husk, the zombie nautilus does not have a unique texture file for its saddle. This inconsistency seems more like an oversight because of the subsequent camel husk saddle definition.

To reproduce: check assets/minecraft/equipment/saddle.json
Expected: a layer at the end named zombie_nautilus_saddle
Observed: no layer listed after zombie_horse_saddle

Note that this is not a feature request requesting a unique texture. The skeleton horse has an identical-looking texture but still has its own equipment definition.