background: fix vignette in overview

We no longer apply background effects when loading backgrounds.

This commit fixes that.

https://bugzilla.gnome.org/show_bug.cgi?id=696712

js/ui/background.js

@@ -241,6 +241,7 @@ const BackgroundCache = new Lang.Class({
         } else {
             this._loadImageContent({ filename: params.filename,
                                      style: params.style,
+                                     effects: params.effects,
                                      cancellable: params.cancellable,
                                      onFinished: params.onFinished });