Some A* and medbot sanity. (#39104)

* Adds some missing astar sanity.

* Also fixes where this came from.

* Actually let's notify when someone does something dumb like this.

code/__HELPERS/AStar.dm

@@ -101,7 +101,10 @@ Actual Adjacent procs :
 	//sanitation
 	var/turf/end = get_turf(_end)
 	var/turf/start = get_turf(caller)
-	if((!start)||(start.z != end.z)||(start == end)) //no pathfinding between z levels
+	if(!start || !end)
+		stack_trace("Invalid A* start or destination")
+		return 0
+	if( start.z != end.z || start == end ) //no pathfinding between z levels
 		return 0
 	if(maxnodes)
 		//if start turf is farther than maxnodes from end turf, no need to do anything

code/modules/mob/living/simple_animal/bot/medbot.dm

@@ -287,7 +287,7 @@
 		oldpatient = patient
 		soft_reset()
 
-	if(!patient)
+	if(QDELETED(patient))
 		if(!shut_up && prob(1))
 			var/list/messagevoice = list("Radar, put a mask on!" = 'sound/voice/mradar.ogg',"There's always a catch, and I'm the best there is." = 'sound/voice/mcatch.ogg',"I knew it, I should've been a plastic surgeon." = 'sound/voice/msurgeon.ogg',"What kind of medbay is this? Everyone's dropping like flies." = 'sound/voice/mflies.ogg',"Delicious!" = 'sound/voice/mdelicious.ogg')
 			var/message = pick(messagevoice)