Advanced mob laziness (#33574)

* Advanced mob laziness

* Compiling fixes for 511

code/controllers/subsystem/idlenpcpool.dm

@@ -1,15 +1,21 @@
 SUBSYSTEM_DEF(idlenpcpool)
 	name = "Idling NPC Pool"
-	flags = SS_POST_FIRE_TIMING|SS_NO_INIT|SS_BACKGROUND
+	flags = SS_POST_FIRE_TIMING|SS_BACKGROUND
 	priority = FIRE_PRIORITY_IDLE_NPC
 	wait = 60
 	runlevels = RUNLEVEL_GAME | RUNLEVEL_POSTGAME
 
 	var/list/currentrun = list()
+	var/static/list/idle_mobs_by_zlevel[][]
 
 /datum/controller/subsystem/idlenpcpool/stat_entry()
 	var/list/idlelist = GLOB.simple_animals[AI_IDLE]
-	..("IdleNPCS:[idlelist.len]")
+	var/list/zlist = GLOB.simple_animals[AI_Z_OFF]
+	..("IdleNPCS:[idlelist.len]|Z:[zlist.len]")
+
+/datum/controller/subsystem/idlenpcpool/Initialize(start_timeofday)
+	idle_mobs_by_zlevel = new /list(world.maxz,0)
+	return ..()
 
 /datum/controller/subsystem/idlenpcpool/fire(resumed = FALSE)
 
@@ -24,6 +30,9 @@ SUBSYSTEM_DEF(idlenpcpool)
 	while(currentrun.len)
 		var/mob/living/simple_animal/SA = currentrun[currentrun.len]
 		--currentrun.len
+		if (!SA)
+			GLOB.simple_animals[AI_IDLE] -= SA
+			continue
 
 		if(!SA.ckey)
 			if(SA.stat != DEAD)