Use task.imported_items() instead of task.items to avoid crashes

beetbox/beets#2537

Author: Hamuko

beetsplug/mpdqueue.py

@@ -132,7 +132,7 @@ def import_task_files(self, task, session):
             return
 
         tracks = []
-        items = sorted(task.items, key=lambda x: x.track)
+        items = sorted(task.imported_items(), key=lambda x: x.track)
         for item in items:
             destination = item.destination(fragment=True)
             self._log.debug(u'{0} will be added to queue', destination)