st-scroll-view-fade: Refuse to work without GLSL

Disable the effect when GLSL is not available otherwise we will
crash later.

https://bugzilla.gnome.org/show_bug.cgi?id=733623

src/st/st-scroll-view-fade.c

@@ -191,6 +191,15 @@ st_scroll_view_fade_set_actor (ClutterActorMeta *meta,
 
   g_return_if_fail (actor == NULL || ST_IS_SCROLL_VIEW (actor));
 
+  if (!clutter_feature_available (CLUTTER_FEATURE_SHADERS_GLSL))
+    {
+      /* if we don't have support for GLSL shaders then we
+       * forcibly disable the ActorMeta
+       */
+      clutter_actor_meta_set_enabled (meta, FALSE);
+      return;
+    }
+
   if (self->vadjustment)
     {
       g_signal_handlers_disconnect_by_func (self->vadjustment,