[gnome-control-center] background: Better guards for public functions

[Bastien Nocera <hadess src gnome org>]

commit ed425ecf9dc7b8e7b65f112a6a5122c83973adae
Author: Bastien Nocera <hadess hadess net>
Date:   Fri Feb 11 03:18:22 2011 +0000

    background: Better guards for public functions

 panels/background/cc-background-item.c |    7 ++++++-
 1 files changed, 6 insertions(+), 1 deletions(-)
---
diff --git a/panels/background/cc-background-item.c b/panels/background/cc-background-item.c
index cfd40fd..414af55 100644
--- a/panels/background/cc-background-item.c
+++ b/panels/background/cc-background-item.c
@@ -173,6 +173,8 @@ cc_background_item_changes_with_time (CcBackgroundItem *item)
 {
         gboolean changes;
 
+	g_return_val_if_fail (CC_IS_BACKGROUND_ITEM (item), FALSE);
+
         changes = FALSE;
         if (item->priv->bg != NULL) {
                 changes = gnome_bg_changes_with_time (item->priv->bg);
@@ -211,6 +213,9 @@ cc_background_item_get_frame_thumbnail (CcBackgroundItem             *item,
         GdkPixbuf *pixbuf = NULL;
         GIcon *icon = NULL;
 
+	g_return_val_if_fail (CC_IS_BACKGROUND_ITEM (item), NULL);
+	g_return_val_if_fail (width > 0 && height > 0, NULL);
+
         set_bg_properties (item);
 
         if (frame >= 0)
@@ -338,7 +343,7 @@ gboolean
 cc_background_item_load (CcBackgroundItem *item,
 			 GFileInfo        *info)
 {
-        g_return_val_if_fail (item != NULL, FALSE);
+        g_return_val_if_fail (CC_IS_BACKGROUND_ITEM (item), FALSE);
         g_return_val_if_fail (item->priv->filename != NULL, FALSE);
 
         update_info (item, info);