Fix a silent traceback in the otr plugin

(the “X has not enabled OTR after n seconds.” would not be displayed)

plugins/otr.py

@@ -882,6 +882,7 @@ class Plugin(BasePlugin):
         else:
             was_locked = False
         def notify_otr_timeout():
+            nonlocal name
             otr = self.get_context(name)
             if isinstance(tab, DynamicConversationTab) and not was_locked:
                 if tab.locked_resource: