[totem-pl-parser] disc: Avoid warnings when the volume doesn't have a mount

[Bastien Nocera <hadess src gnome org>]

commit 4ba8cc2d94c1721f9310370db3452337f51c4d9a
Author: Bastien Nocera <hadess hadess net>
Date:   Fri Mar 29 17:37:36 2013 +0100

    disc: Avoid warnings when the volume doesn't have a mount

 plparse/totem-disc.c |    6 ++++--
 1 files changed, 4 insertions(+), 2 deletions(-)
---
diff --git a/plparse/totem-disc.c b/plparse/totem-disc.c
index 3e81d74..d480ee5 100644
--- a/plparse/totem-disc.c
+++ b/plparse/totem-disc.c
@@ -429,8 +429,10 @@ cd_cache_new (const char *dev,
     GMount *mount;
 
     mount = g_volume_get_mount (volume);
-    cache->content_types = g_mount_guess_content_type_sync (mount, FALSE, NULL, NULL);
-    g_object_unref (mount);
+    if (mount) {
+      cache->content_types = g_mount_guess_content_type_sync (mount, FALSE, NULL, NULL);
+      g_object_unref (mount);
+    }
   }
 
   return cache;