Fixed WebSocket connection hang issue after listener reconfigure.

Because the configuration values were read from the listener's configuration,
an established WebSocket connection was unable to work properly (i. e. stuck)
if the listener was removed.  The correct source of configuration values is the
request config joint.

This is related to issue #581 on GitHub.

test/test_asgi_websockets.py

@@ -1481,3 +1481,20 @@ class TestASGIWebsockets(TestApplicationPython):
         self.check_frame(frame, True, self.ws.OP_PING, '')  # PING frame
 
         sock.close()
+
+    def test_asgi_websockets_client_locks_app(self):
+        self.load('websockets/mirror')
+
+        message = 'blah'
+
+        _, sock, _ = self.ws.upgrade()
+
+        assert 'success' in self.conf({}), 'remove app'
+
+        self.ws.frame_write(sock, self.ws.OP_TEXT, message)
+
+        frame = self.ws.frame_read(sock)
+
+        assert message == frame['data'].decode('utf-8'), 'client'
+
+        sock.close()