[gtk+/portal] Make sure fd is positive

[Matthias Clasen <matthiasc src gnome org>]

commit 6c68572c1e0192973a2336289782ce8ef740f496
Author: Matthias Clasen <mclasen redhat com>
Date:   Wed Jul 6 21:37:55 2016 -0400

    Make sure fd is positive

 gtk/gtkprintjob.c |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)
---
diff --git a/gtk/gtkprintjob.c b/gtk/gtkprintjob.c
index b53f46f..571d2b0 100644
--- a/gtk/gtkprintjob.c
+++ b/gtk/gtkprintjob.c
@@ -469,6 +469,7 @@ gtk_print_job_set_source_fd (GtkPrintJob  *job,
                              GError      **error)
 {
   g_return_val_if_fail (GTK_IS_PRINT_JOB (job), FALSE);
+  g_return_val_if_fail (fd >= 0, FALSE);
 
   job->priv->spool_io = g_io_channel_unix_new (fd);
   if (g_io_channel_set_encoding (job->priv->spool_io, NULL, error) != G_IO_STATUS_NORMAL)