[gnome-software] trivial: Fix tiny warning spotted with clang

[Richard Hughes <rhughes src gnome org>]

commit 100b4c0e395370ac1b718c9e02540d37cbfa1601
Author: Richard Hughes <richard hughsie com>
Date:   Wed Feb 17 11:55:16 2016 +0000

    trivial: Fix tiny warning spotted with clang

 src/plugins/gs-plugin-fwupd.c |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)
---
diff --git a/src/plugins/gs-plugin-fwupd.c b/src/plugins/gs-plugin-fwupd.c
index 36cf7f4..43acecf 100644
--- a/src/plugins/gs-plugin-fwupd.c
+++ b/src/plugins/gs-plugin-fwupd.c
@@ -555,6 +555,7 @@ gs_plugin_fwupd_update_lvfs_metadata (const gchar *data_fn, const gchar *sig_fn,
        /* set out of band file descriptor */
        fd_list = g_unix_fd_list_new ();
        retval = g_unix_fd_list_append (fd_list, fd_data, NULL);
+       g_assert (retval != -1);
        retval = g_unix_fd_list_append (fd_list, fd_sig, NULL);
        g_assert (retval != -1);
        request = g_dbus_message_new_method_call (FWUPD_DBUS_SERVICE,