[rygel] media-export: Fix crash on unknown QueryContainer

[Jens Georg <jensgeorg src gnome org>]

commit 6755a280d0d537f517a53466c3bbbc3113a47943
Author: Jens Georg <mail jensge org>
Date:   Sun Aug 12 17:52:49 2012 +0200

    media-export: Fix crash on unknown QueryContainer
    
    Previously get_by_id would return an empty id, leading in a null
    container on which we tried to set the parent.

 ...rygel-media-export-query-container-factory.vala |    7 +++++--
 .../rygel-media-export-root-container.vala         |    4 +++-
 2 files changed, 8 insertions(+), 3 deletions(-)
---
diff --git a/src/plugins/media-export/rygel-media-export-query-container-factory.vala b/src/plugins/media-export/rygel-media-export-query-container-factory.vala
index 3a6e632..cc1075c 100644
--- a/src/plugins/media-export/rygel-media-export-query-container-factory.vala
+++ b/src/plugins/media-export/rygel-media-export-query-container-factory.vala
@@ -85,12 +85,15 @@ internal class Rygel.MediaExport.QueryContainerFactory : Object {
      * @param name  An the title of the container. If not supplied, it will
      *              be derived from the plain-text description of the
      *              container
-     * @return A new instance of QueryContainer
+     * @return A new instance of QueryContainer or null if id does not exist
      */
-    public QueryContainer create_from_id (MediaCache cache,
+    public QueryContainer? create_from_id (MediaCache cache,
                                           string     id,
                                           string     name = "") {
         var definition = this.get_virtual_container_definition (id);
+        if (definition == null) {
+            return null;
+        }
 
         return this.create_from_description (cache, definition, name);
     }
diff --git a/src/plugins/media-export/rygel-media-export-root-container.vala b/src/plugins/media-export/rygel-media-export-root-container.vala
index 3b15685..753e72f 100644
--- a/src/plugins/media-export/rygel-media-export-root-container.vala
+++ b/src/plugins/media-export/rygel-media-export-root-container.vala
@@ -125,7 +125,9 @@ public class Rygel.MediaExport.RootContainer : Rygel.MediaExport.DBContainer {
         if (object == null && id.has_prefix (QueryContainer.PREFIX)) {
             var factory = QueryContainerFactory.get_default ();
             var container = factory.create_from_id (this.media_db, id);
-            container.parent = this;
+            if (container != null) {
+                container.parent = this;
+            }
 
             return container;
         }