[gnome-screensaver] dialog: Fix crash in user switcher code

[Ray Strode <halfline src gnome org>]

commit 338b86c4f0c2cdc4241dbf5cda913f0184afc105
Author: Huzaifa Sidhpurwala <huzaifas redhat com>
Date:   Tue Apr 26 13:15:56 2011 -0400

    dialog: Fix crash in user switcher code
    
    The user switch button currently causes the lock dialog to crash
    because of an inverted conditional in the error checking code.
    
    This commit addresses the crash by performing the proper check
    in the conditional.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=648234

 src/gs-lock-plug.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/src/gs-lock-plug.c b/src/gs-lock-plug.c
index 67ab36a..6706fde 100644
--- a/src/gs-lock-plug.c
+++ b/src/gs-lock-plug.c
@@ -167,7 +167,7 @@ do_user_switch (GSLockPlug *plug)
         g_object_unref (context);
         g_object_unref (app);
 
-        if (!error) {
+        if (error != NULL) {
                 gs_debug ("Unable to start GDM greeter: %s", error->message);
                 g_error_free (error);
         }