Fix icon caching - set size in cache key

We need to include the icon size in the data we pass to on_pixbuf_loaded()
so that we can include it in the key we use when caching the icon
Currently we save icons in the cache at size 0 but look them up at size 48
so no caching occurs.

http://bugzilla.gnome.org/show_bug.cgi?id=583503

src/shell-texture-cache.c

@@ -539,6 +539,7 @@ shell_texture_cache_load_gicon (ShellTextureCache *cache,
           data->icon = icon;
           data->icon_info = info;
           data->texture = g_object_ref (texture);
+          data->width = data->height = size;
           load_icon_pixbuf_async (cache, icon, info, size, NULL, on_pixbuf_loaded, data);
         }
     }