Wanda: don't recreate the texture if the icon size doesn't change

Wanda flickers if the animation is recreated, but we don't need to if
the size doesn't change (as we're not affected by icon theme changes).

https://bugzilla.gnome.org/show_bug.cgi?id=684154

js/ui/wanda.js

@@ -77,11 +77,16 @@ const WandaIcon = new Lang.Class({
             }
         }));
 
-        this._i = 0;
-
         return this._animations;
     },
 
+    _createIconTexture: function(size) {
+        if (size == this.iconSize)
+            return;
+
+        this.parent(size);
+    },
+
     _update: function() {
         let n = this._animations.get_n_children();
         if (n == 0) {