Do not fail if _ is not defined

weblate/trans/models.py

@@ -36,7 +36,7 @@ def ttkit(storefile):
 
     # Workaround for _ created by interactive interpreter and
     # later used instead of gettext by ttkit
-    if not callable(__builtin__.__dict__['_']):
+    if '_' in __builtin__.__dict__ and not callable(__builtin__.__dict__['_']):
         del __builtin__.__dict__['_']
 
     # Add missing mode attribute to Django file wrapper