[gupnp] service: Fix adding call-back to list

[Jens Georg <jensgeorg src gnome org>]

commit a1edc424d9e4981fc805130145df7582888057d1
Author: Jens Georg <mail jensge org>
Date:   Wed Jun 17 15:31:31 2020 +0200

    service: Fix adding call-back to list

 libgupnp/gupnp-service.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)
---
diff --git a/libgupnp/gupnp-service.c b/libgupnp/gupnp-service.c
index ed025af..cf90a0c 100644
--- a/libgupnp/gupnp-service.c
+++ b/libgupnp/gupnp-service.c
@@ -1247,7 +1247,9 @@ subscribe (GUPnPService *service,
                         // Also one part of CVE-2020-12695 mitigation - limit URI length
                         // UPnP does not impose any restrictions here
                         if (strlen (start) <= 256) {
-                                add_subscription_callback (context, data->callbacks, start);
+                                data->callbacks = add_subscription_callback (context,
+                                                                             data->callbacks,
+                                                                             start);
                         } else {
                                 g_warning ("Subscription URI exceeds recommended length "
                                            "of 256 bytes, skipping");