Correct variable name

Author: ids1024

mps_youtube/content.py

@@ -55,7 +55,7 @@ def __init__(self, items, length=None, msg=None, failmsg=None, loadmsg=None):
         self._items = items
         self._length = length
         if length is None:
-            self._length = len(songs)
+            self._length = len(items)
         self._msg = msg
         self._failmsg = failmsg
         self._loadmsg = loadmsg