[gnome-shell] background: fix typo updating images for animated background

[Giovanni Campagna <gcampagna src gnome org>]

commit b742b1eed23a8f8cdda001c8f05b1da5449694bb
Author: Giovanni Campagna <gcampagna src gnome org>
Date:   Thu Jun 26 18:25:14 2014 +0200

    background: fix typo updating images for animated background
    
    We must remove the old image from the cache, not the new one.
    
    This was causing a leak of old (and expensive) background
    images, and was causing errors at the end of animations, trying
    to destroy the animated background.

 js/ui/background.js |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/js/ui/background.js b/js/ui/background.js
index 3cdc7ef..3730beb 100644
--- a/js/ui/background.js
+++ b/js/ui/background.js
@@ -448,7 +448,7 @@ const Background = new Lang.Class({
 
         let image = this._images[index];
         if (image.content)
-            this._cache.removeImageContent(content);
+            this._cache.removeImageContent(image.content);
         image.content = content;
         this._watchCacheFile(filename);
     },