[babl] assigned_name can be NULL, causing segfault

[Mukund Sivaraman <muks src gnome org>]

commit cb2355ec2940fce332b589c87acb4f6d8a7616f7
Author: Mukund Sivaraman <muks banu com>
Date:   Thu Feb 26 20:07:46 2015 +0530

    assigned_name can be NULL, causing segfault

 babl/babl-model.c |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)
---
diff --git a/babl/babl-model.c b/babl/babl-model.c
index 4c995df..bb7b734 100644
--- a/babl/babl-model.c
+++ b/babl/babl-model.c
@@ -170,7 +170,8 @@ babl_model_new (void *first_argument,
 
       else
         {
-          babl_fatal ("unhandled argument '%s' for babl_model '%s'", arg, assigned_name);
+          babl_fatal ("unhandled argument '%s' for babl_model '%s'",
+                     arg, assigned_name ? assigned_name : "(unnamed)");
         }
 
       arg = va_arg (varg, char *);