[meld] meldwindow: Clean up tab switching state variables

[Kai Willadsen <kaiw src gnome org>]

commit 263e6bce522963c8b8c880ed94a8ea0d49b50d7c
Author: Kai Willadsen <kai willadsen gmail com>
Date:   Sun Dec 13 07:13:38 2015 +1000

    meldwindow: Clean up tab switching state variables

 meld/meldwindow.py |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)
---
diff --git a/meld/meldwindow.py b/meld/meldwindow.py
index 62fdef6..a2bd1c6 100644
--- a/meld/meldwindow.py
+++ b/meld/meldwindow.py
@@ -543,6 +543,8 @@ class MeldWindow(gnomeglade.Component):
         if self.tab_switch_merge_id:
             self.ui.remove_ui(self.tab_switch_merge_id)
             self.ui.remove_action_group(self.tab_switch_actiongroup)
+            self.tab_switch_merge_id = None
+            self.tab_switch_actiongroup = None
 
         self.tab_switch_merge_id = self.ui.new_merge_id()
         self.tab_switch_actiongroup = Gtk.ActionGroup(name="TabSwitchActions")