<Someone> reported being swallowed by his pet purple worm during
Conflict, then being stuck inside once Conflict ended. I'm not entirely
sure what dog_move() intended by the "swallowed case handled above" comment.
It returns without letting the pet move when the distance between pet and
hero is 0; that wasn't much in the way of "handling" being swallowed.
Grabbing pets did let go, but peaceful monsters didn't until you actually
attempted to move away from them. Now all four combinations (grabbed or
swallowed by tame or peaceful monster) are handled the same: the monster
will let the hero go next time it gets a chance to try to move, using up
its move in the process.