[gnome-software] Avoid a critical on shutdown

[Matthias Clasen <matthiasc src gnome org>]

commit 84158baa1374bae294ca3ab27321f29add15f735
Author: Matthias Clasen <mclasen redhat com>
Date:   Thu Aug 29 19:01:30 2013 -0400

    Avoid a critical on shutdown
    
    The category may not be set if we've never switched to the category
    page.

 src/gs-shell-category.c |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)
---
diff --git a/src/gs-shell-category.c b/src/gs-shell-category.c
index a85f764..feaead4 100644
--- a/src/gs-shell-category.c
+++ b/src/gs-shell-category.c
@@ -266,7 +266,8 @@ gs_shell_category_finalize (GObject *object)
        GsShellCategoryPrivate *priv = shell->priv;
 
        g_object_unref (priv->builder);
-        g_object_unref (priv->category);
+        if (priv->category)
+                g_object_unref (priv->category);
 
        G_OBJECT_CLASS (gs_shell_category_parent_class)->finalize (object);
 }