Make AI restalk players after they respawn

[Ansible2]

Currently, if a player respawns they are not stalked again and the enemies that were stalking them are shifted to other players.

If all players have respawned, all AI will go into a patrol mode and won't restalk anyone.

Adjust this to have AI stalk players again after respawn (and a decent delay).

[Ansible2]

Added in #642