[rygel] renderer-get: Prevent critical

[Jens Georg <jensgeorg src gnome org>]

commit 011a9bb23bf7c4d2114ffb52662ed5e8041108c8
Author: Jens Georg <mail jensge org>
Date:   Sun May 10 16:06:06 2015 +0200

    renderer-get: Prevent critical
    
    Signed-off-by: Jens Georg <mail jensge org>

 .../rygel-playbin-player.vala                      |    5 +++--
 1 files changed, 3 insertions(+), 2 deletions(-)
---
diff --git a/src/librygel-renderer-gst/rygel-playbin-player.vala 
b/src/librygel-renderer-gst/rygel-playbin-player.vala
index cf4300a..a78996f 100644
--- a/src/librygel-renderer-gst/rygel-playbin-player.vala
+++ b/src/librygel-renderer-gst/rygel-playbin-player.vala
@@ -347,9 +347,10 @@ public class Rygel.Playbin.Player : GLib.Object, Rygel.MediaPlayer {
 
     public int64 byte_position {
        get {
-            int64 pos;
+            int64 pos = 0;
 
-            if (this.playbin.source.query_position (Format.BYTES, out pos)) {
+            if (this.playbin.source != null &&
+                this.playbin.source.query_position (Format.BYTES, out pos)) {
                 return pos;
             } else {
                 return 0;