Use a for loop instead of map in the join info event.

map returns an iterator on python3, the function won't get executed
unless we ask for the result, since the function doesn't return a result
we'll use a for loop instead of complicating things unnecessarily.

matrix/events.py

@@ -425,7 +425,8 @@ class MatrixSyncEvent(MatrixEvent):
             server.sync()
             return
 
-        map(self._execute_joined_info, self.joined_room_infos)
+        for room_info in self.joined_room_infos:
+            self._execute_joined_info(room_info)
 
         server.next_batch = self.next_batch
         server.sync()