proxy: use a core sync to know when Props have been enumerated

This is necessary to finish augmenting nodes that advertise
PropInfo & Props in their param info but they don't actually have
any properties, so there is no param event emitted
(ex. the jack device nodes)

Because the sync is synchronous with the calls over the protocol,
the callback is ensured to be called after all the param events
have been emitted

lib/wp/proxy.c

@@ -284,6 +284,18 @@ wp_proxy_get_gobj_property (GObject * object, guint property_id, GValue * value,
   }
 }
 
+static void
+wp_proxy_enum_props_done (WpCore * core, GAsyncResult * res, WpProxy * self)
+{
+  g_autoptr (GError) error = NULL;
+  if (!wp_core_sync_finish (core, res, &error)) {
+    wp_warning_object (self, "core sync failed: %s", error->message);
+  }
+
+  wp_trace_object (self, "enum props done");
+  wp_proxy_set_feature_ready (self, WP_PROXY_FEATURE_PROPS);
+}
+
 static void
 wp_proxy_enable_feature_props (WpProxy * self)
 {
@@ -303,6 +315,8 @@ wp_proxy_enable_feature_props (WpProxy * self)
   }
 
   if (have_propinfo && have_props) {
+    g_autoptr (WpCore) core = wp_proxy_get_core (self);
+
     if (!klass->enum_params || !klass->subscribe_params) {
       wp_proxy_augment_error (self, g_error_new (WP_DOMAIN_LIBRARY,
             WP_LIBRARY_ERROR_INVARIANT,
@@ -312,6 +326,8 @@ wp_proxy_enable_feature_props (WpProxy * self)
 
     klass->enum_params (self, SPA_PARAM_PropInfo, 0, -1, NULL);
     klass->subscribe_params (self, ids, SPA_N_ELEMENTS (ids));
+    wp_core_sync (core, NULL, (GAsyncReadyCallback) wp_proxy_enum_props_done,
+        self);
   } else {
     /* declare as ready with no props */
     wp_proxy_set_feature_ready (self, WP_PROXY_FEATURE_PROPS);
@@ -1085,10 +1101,6 @@ wp_proxy_handle_event_param (void * proxy, int seq, uint32_t id,
         wp_trace_boxed (WP_TYPE_SPA_POD, w_param,
             "storing Props on " WP_OBJECT_FORMAT, WP_OBJECT_ARGS (self));
         wp_props_store (priv->props, NULL, g_steal_pointer (&w_param));
-
-        /* we receive PropInfo before Props; once we get Props, we know we have
-           completed caching of props, so the feature is ready */
-        wp_proxy_set_feature_ready (self, WP_PROXY_FEATURE_PROPS);
         break;
       default:
         break;