[gdk-pixbuf] Add a better diagnostic message

[Matthias Clasen <matthiasc src gnome org>]

commit 5f726772149809a65bd9d15e7817fa94e272fafe
Author: Matthias Clasen <mclasen redhat com>
Date:   Fri May 31 20:10:38 2013 -0400

    Add a better diagnostic message
    
    This test is falling on the builder, but the message
    doesn't help to find out why.

 tests/pixbuf-threads.c |    6 +++++-
 1 files changed, 5 insertions(+), 1 deletions(-)
---
diff --git a/tests/pixbuf-threads.c b/tests/pixbuf-threads.c
index e9ae41a..268b01f 100644
--- a/tests/pixbuf-threads.c
+++ b/tests/pixbuf-threads.c
@@ -43,7 +43,11 @@ load_image (gpointer  data,
   loader = gdk_pixbuf_loader_new ();
 
   file = fopen (filename, "r");
-  g_assert (file);
+  if (!file)
+    {
+      g_warning ("failed to open %s\n", filename);
+      g_assert_not_reached ();
+    }
 
   if (verbose) g_print ("%p start image %s\n", self, filename);
   while (!feof (file))