[gnome-settings-daemon/gnome-3-16] power: Fix invalid error access

[Bastien Nocera <hadess src gnome org>]

commit b11fac15529967dec20215ddda61da11fe5adbf7
Author: Bastien Nocera <hadess hadess net>
Date:   Tue May 26 11:56:41 2015 +0200

    power: Fix invalid error access
    
    From coverity:
    gnome-settings-daemon-3.14.4/plugins/power/gpm-common.c:321:52: warning: Access to field 'message' 
results in a dereference of a null pointer (loaded from variable 'error')
    
    https://bugzilla.gnome.org/show_bug.cgi?id=749882

 plugins/power/gpm-common.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/plugins/power/gpm-common.c b/plugins/power/gpm-common.c
index e8769ca..ed962e2 100644
--- a/plugins/power/gpm-common.c
+++ b/plugins/power/gpm-common.c
@@ -338,7 +338,7 @@ backlight_set_mock_value (gint value)
 
        filename = "GSD_MOCK_brightness";
        contents = g_strdup_printf ("%d", value);
-       if (!g_file_set_contents (filename, contents, -1, NULL))
+       if (!g_file_set_contents (filename, contents, -1, &error))
                g_warning ("Setting mock brightness failed: %s", error->message);
        g_clear_error (&error);
        g_free (contents);