[meld] Fix recent comparison crashing on single VC file open

[Kai Willadsen <kaiw src gnome org>]

commit e4a2ea47885d0f77f2504fd41e5cddc5c5e872a3
Author: Kai Willadsen <kai willadsen gmail com>
Date:   Mon Dec 17 05:11:49 2012 +1000

    Fix recent comparison crashing on single VC file open

 meld/meldwindow.py |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)
---
diff --git a/meld/meldwindow.py b/meld/meldwindow.py
index 41cb1e9..7672622 100644
--- a/meld/meldwindow.py
+++ b/meld/meldwindow.py
@@ -730,7 +730,8 @@ class MeldWindow(gnomeglade.Component):
 
         elif len(paths) in (2, 3):
             tab = self.append_diff(paths, auto_compare, auto_merge)
-        app.recent_comparisons.add(tab)
+        if tab:
+            app.recent_comparisons.add(tab)
         return tab
 
     def current_doc(self):