chameleon/genocide fix (trunk only)

chameleon/genocide fix (trunk only)

     While testing some pending teleport changes, I was baffled by having
my adjacent pet sometimes vanish when accompanying me on a level teleport.
Tracing through parts of execution:  keepdogs() kept it; losedogs() called
mon_arrive() which called place_monster() for it, but then right after that
kill_genocided_monsters() removed it.  Turns out that `kill_cham' was left
uninitialized for the first iteration through the fmon loop (and pet had
always just been inserted as first entry of the fmon list).

     No fixes entry; this revises a post-3.4.3 revision.