apt: debconf-helper: Fix g_object_unref (socket) assertion error

Fixes the following assertion error when "pk-debconf-helper" exits.

Aug 19 19:45:19 debian pk-debconf-help[22042]: g_object_unref: assertion 'G_IS_OBJECT (object)' failed

Refer: PackageKit#886 (comment)

Author: sidt4

lib/packagekit-glib2/pk-client-helper.c

@@ -531,7 +531,7 @@ pk_client_helper_start_with_socket (PkClientHelper *client_helper,
 	priv->envp = g_strdupv (envp);
 
 	/* Set the socket */
-	priv->socket = socket;
+	g_set_object (&priv->socket, socket);
 
 	/* socket has data */
 	fd = g_socket_get_fd (priv->socket);