Observer fixups.

Adds a proper proc for raising events.
Now only creates the observer lists when an object registers itself.
Multitools now unregister themselves properly from buffers on Destroy().

code/controllers/observer_listener/datum/observer.dm

@@ -4,28 +4,38 @@
 	var/list/observer_events
 
 /datum/Destroy()
-	var/list/destroy_listeners = get_listener_list_from_event(OBSERVER_EVENT_DESTROY)
-	if(destroy_listeners)
-		for(var/destroy_listener in destroy_listeners)
-			call(destroy_listener, destroy_listeners[destroy_listener])(src)
-
+	raise_event(OBSERVER_EVENT_DESTROY, list(src))
 	for(var/list/listeners in observer_events)
 		listeners.Cut()
 
 	return ..()
 
 /datum/proc/register(var/event, var/procOwner, var/proc_call)
-	var/list/listeners = get_listener_list_from_event(event)
+	var/list/listeners = get_listener_list_from_event(event, TRUE)
 	listeners[procOwner] = proc_call
 
 /datum/proc/unregister(var/event, var/procOwner)
-	var/list/listeners = get_listener_list_from_event(event)
+	var/list/listeners = get_listener_list_from_event(event, FALSE)
 	listeners -= procOwner
 
-/datum/proc/get_listener_list_from_event(var/observer_event)
-	if(!observer_events) observer_events = list()
+/datum/proc/raise_event(var/event, var/list/args = list())
+	var/list/listeners = get_listener_list_from_event(event, FALSE)
+	if(listeners)
+		for(var/listener in listeners)
+			call(listener, listeners[listener])(arglist(args))
+
+/datum/proc/get_listener_list_from_event(var/observer_event, var/create_list)
+	if(!observer_events)
+		if(create_list)
+			observer_events = list()
+		else
+			return
+
 	var/list/listeners = observer_events[observer_event]
 	if(!listeners)
-		listeners = list()
-		observer_events[observer_event] = listeners
+		if(create_list)
+			listeners = list()
+			observer_events[observer_event] = listeners
+		else
+			return
 	return listeners