line sorting fails if no lines selected

[gorilych]

This is zim 0.65
Platform: nt
Locale: en_US cp1252
FS encoding: mbcs
Python: (2, 7, 11, 'final', 0)
Gtk: (2, 24, 10)
Pygtk: (2, 24, 0)
Zim revision is:
  branch: 065
  revision: 805 <email address hidden>
  date: 2015-11-01 15:42:45 +0100

======= Traceback =======
  File "zim\actions.pyo", line 109, in func
  File "zim\plugins\linesorter.pyo", line 57, in sort_selected_lines
AttributeError: 'MainWindowExtension' object has no attribute 'ui'

looks like a typo on line 57:

  MessageDialog(self.ui,

it should be self.window, I believe