Fix crash when Arch-vile resurrects after save

Potential crash after loading a savegame and Arch-vile's target is still
null when it resurrects a monster. Still subtract one from the player's
kill count since the monster isn't dead anymore.
Lost Souls spawned by a PE wouldn't infight

Lost Souls spawned by a Pain Elemental wouldn't infight after player
death, since their MF_COUNTKILL flag has been removed.