Noticed whlie testing the steed-in-pit fix. The EXTRA_SANITY_CHECKS
for remove_monster() are being tripped if riding hero has steed killed
out from under him because the steed is not on the map. This started
out simple but got a bit complicated. It seems to be sufficient but
I'm not very confident about it.
Being engulfed while mounted gave "placing monster over another?" due
to a change made along with EXTRA_SANITY_CHECKS but not conditional on
it. (The change was to issue a warning about an actual problem which
was previously undiagnosed.) I think bumping the engulfer off the map
in favor of the former steed only worked because some u.uswallow code
eventually used the hero's location to put the engulfer back. I didn't
pursue that to try to figure what really happened, just prevent it.
The DISMOUNT_BONES handling was being executed even if the steed was
dead. DISMOUNT_BONES only happens if the hero is dead. Since I don't
know whether it's possible for dead hero and dead steed to happen at
the same time, move it inside the steed-not-dead block just in case.
be327d9822