[gnome-documents] Fix warning introduced by previous patch

[William Jon McCann <mccann src gnome org>]

commit b433f4e92311eb43f1ddb90e2abecb63568d2384
Author: William Jon McCann <jmccann redhat com>
Date:   Sun Jan 6 03:25:40 2013 -0500

    Fix warning introduced by previous patch

 src/lib/gd-nav-bar.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/src/lib/gd-nav-bar.c b/src/lib/gd-nav-bar.c
index de52097..f740a5a 100644
--- a/src/lib/gd-nav-bar.c
+++ b/src/lib/gd-nav-bar.c
@@ -474,7 +474,7 @@ gd_nav_bar_document_changed_cb (EvDocumentModel *model,
         priv->page_start = -1;
         priv->page_end = -1;
 
-        g_object_unref (priv->document);
+        g_clear_object (&priv->document);
         priv->document = document;
         if (priv->document != NULL) {
                 g_object_ref (priv->document);