Fixes npcpool runtime (#52347)

* Fixes npcpool runtime

* Adds comment

* added warnings for real this time

code/controllers/subsystem/idlenpcpool.dm

@@ -34,6 +34,7 @@ SUBSYSTEM_DEF(idlenpcpool)
 		--currentrun.len
 		if (!SA)
 			GLOB.simple_animals[AI_IDLE] -= SA
+			log_world("Found a null in simple_animals list!")
 			continue
 
 		if(!SA.ckey)

code/controllers/subsystem/npcpool.dm

@@ -23,6 +23,11 @@ SUBSYSTEM_DEF(npcpool)
 		var/mob/living/simple_animal/SA = currentrun[currentrun.len]
 		--currentrun.len
 
+		if (!SA) // Some issue causes nulls to get into this list some times. This keeps it running, but the bug is still there.
+			GLOB.simple_animals[AI_ON] -= SA
+			log_world("Found a null in simple_animals list!")
+			continue
+
 		if(!SA.ckey && !SA.notransform)
 			if(SA.stat != DEAD)
 				SA.handle_automated_movement()