define signal before starting zc thread

Shared/lib/python3.4/site-packages/zeroconf.py

@@ -971,10 +971,11 @@ class ServiceBrowser(threading.Thread):
 
         self.done = False
 
+        self._service_state_changed = Signal()
+
         self.zc.add_listener(self, DNSQuestion(self.type, _TYPE_PTR, _CLASS_IN))
         self.start()
 
-        self._service_state_changed = Signal()
 
         if hasattr(handlers, 'add_service'):
             listener = handlers