[rygel] renderer: Prevent critical on empty features

[Jens Georg <jensgeorg src gnome org>]

commit 325b33a7842a1a7f5a47fe0a215c43239b97cb32
Author: Jens Georg <jensg openismus com>
Date:   Thu Jan 31 22:20:14 2013 +0100

    renderer: Prevent critical on empty features

 src/librygel-renderer/rygel-av-transport.vala |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)
---
diff --git a/src/librygel-renderer/rygel-av-transport.vala b/src/librygel-renderer/rygel-av-transport.vala
index ccdd681..616cd09 100644
--- a/src/librygel-renderer/rygel-av-transport.vala
+++ b/src/librygel-renderer/rygel-av-transport.vala
@@ -686,8 +686,8 @@ internal class Rygel.AVTransport : Service {
         return result;
     }
 
-    private bool is_playlist (string mime, string features) {
-        return mime == "text/xml" &&
+    private bool is_playlist (string mime, string? features) {
+        return mime == "text/xml" && features != null &&
                features.has_prefix ("DLNA.ORG_PN=DIDL_S");
     }
 }