Fix an error in the Natlink engine back-end

Related to issue dictation-toolbox#370 and rule contexts.

Author: drmfinlay

dragonfly/engines/backend_natlink/engine.py

@@ -450,7 +450,7 @@ def activate_rule(self, rule_name):
         grammar_object = self.grammar_object
         try:
             grammar_object.activate(rule_name, self.hwnd)
-        except self.natlink.NatError:
+        except self.engine.natlink.NatError:
             grammar_object.deactivate(rule_name)
             grammar_object.activate(rule_name, self.hwnd)