Make tiles work like tilesets - if you ask to be notified and it's already loaded, notify immediately.

git-svn-id: svn+ssh://src.earth.threerings.net/nenya/trunk@968 ed5b42cb-e716-0410-a449-f6a68f950b19

src/as/com/threerings/media/tile/Tile.as

@@ -97,7 +97,11 @@ public class Tile
 
     public function notifyOnLoad (func :Function) :void
     {
-        _notifyOnLoad.push(func);
+        if (_image != null) {
+            func(this);
+        } else {
+            _notifyOnLoad.push(func);
+        }
     }
 
     /**