[gvfs] cdda: Fix warnings for each track on the CD

[Bastien Nocera <hadess src gnome org>]

commit 7855cb474a061b0908a2fa8f4b3687f1d9759e97
Author: Bastien Nocera <hadess hadess net>
Date:   Thu Mar 14 11:38:47 2013 +0100

    cdda: Fix warnings for each track on the CD
    
    (process:22937): GLib-CRITICAL **: g_convert: assertion `str != NULL' failed
    for each of the tracks as we tried to convert the genre (which was NULL)
    
    https://bugzilla.gnome.org/show_bug.cgi?id=695835

 daemon/gvfsbackendcdda.c |    3 +++
 1 files changed, 3 insertions(+), 0 deletions(-)
---
diff --git a/daemon/gvfsbackendcdda.c b/daemon/gvfsbackendcdda.c
index 11c6aea..a8213a8 100644
--- a/daemon/gvfsbackendcdda.c
+++ b/daemon/gvfsbackendcdda.c
@@ -161,6 +161,9 @@ release_metadata (GVfsBackendCdda *cdda_backend)
 static char *
 cdtext_string_to_utf8 (const char *string)
 {
+  if (string == NULL)
+    return NULL;
+
   /* CD-text doesn't specify encoding. In case outside ascii, assume latin-1. */
   return g_convert (string, -1, "UTF-8", "ISO-8859-1", NULL, NULL, NULL);
 }