[gegl] png-load: Fix abort on computing without valid uri/path

[Jon Nordby <jonnor src gnome org>]

commit 216c826cead192994fd4650151b28c46f96da11c
Author: Jon Nordby <jononor gmail com>
Date:   Mon Nov 10 06:56:27 2014 +0100

    png-load: Fix abort on computing without valid uri/path
    
    Overeager error checking :)

 operations/external/png-load.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/operations/external/png-load.c b/operations/external/png-load.c
index 3f91eb4..c623d01 100644
--- a/operations/external/png-load.c
+++ b/operations/external/png-load.c
@@ -421,11 +421,11 @@ get_bounding_box (GeglOperation *operation)
 
   GInputStream *stream = gegl_gio_open_input_stream(o->uri, o->path, &infile, &err);
   WARN_IF_ERROR(err);
+  if (!stream) return;
   status = query_png(stream, &width, &height, &format, &err);
   WARN_IF_ERROR(err);
   g_input_stream_close(stream, NULL, NULL);
 
-  g_assert(status == 0);
   if (status)
     {
       width = 0;