[gegl] svg-load: avoid crashing on error without gerror set

[Øyvind Kolås <ok src gnome org>]

commit 0fb072e0c853d133d596ec0a1a18049a71eaefbc
Author: Øyvind Kolås <pippin gimp org>
Date:   Sun Mar 12 20:49:43 2017 +0100

    svg-load: avoid crashing on error without gerror set

 operations/external/svg-load.c |    7 +++++--
 1 files changed, 5 insertions(+), 2 deletions(-)
---
diff --git a/operations/external/svg-load.c b/operations/external/svg-load.c
index cce7c54..1215555 100644
--- a/operations/external/svg-load.c
+++ b/operations/external/svg-load.c
@@ -162,8 +162,11 @@ prepare (GeglOperation *operation)
       stream = gegl_gio_open_input_stream (o->uri, o->path, &p->file, &error);
       if (stream == NULL)
         {
-          g_warning ("%s", error->message);
-          g_error_free (error);
+          if (error)
+            {
+              g_warning ("%s", error->message);
+              g_error_free (error);
+            }
           cleanup (operation);
           return;
         }