Update __init__.py (#4877)

Cleaner exit by not throwing exception if server was not set during initialization of component (ref https://github.com/home-assistant/home-assistant/pull/4866)

homeassistant/components/http/__init__.py

@@ -323,9 +323,11 @@ class HomeAssistantWSGI(object):
     @asyncio.coroutine
     def stop(self):
         """Stop the wsgi server."""
+        if self.server:
             self.server.close()
             yield from self.server.wait_closed()
         yield from self.app.shutdown()
+        if self._handler:
             yield from self._handler.finish_connections(60.0)
         yield from self.app.cleanup()