ocarina: Use libsaria.sources.cur_id for scrolling

I was using a get_attrs() call for finding the current song id.  This
information is available directly through libsaria.sources, though.  I
think it will be easier to just use the cur_id variable.

ocarina/sources/listview.py

@@ -95,8 +95,8 @@ class ListView(gtk.TreeView):
 		self.thaw()
 
 	def goto(self, *args):
-		id = libsaria.sources.get_attrs("id")
-		if id == -1: # Bad id
+		id = libsaria.sources.cur_id
+		if id == None or id == -1: # Bad id
 			return
 		vis = self.get_visible_rect()
 		if vis[3] == 0: # The widget hasn't been realized yet