Move collection change bind to LoadComplete

Best practice anyways

osu.Game/Skinning/SkinProvidingContainer.cs

@@ -65,6 +65,11 @@ namespace osu.Game.Skinning
         protected SkinProvidingContainer()
         {
             RelativeSizeAxes = Axes.Both;
+        }
+
+        protected override void LoadComplete()
+        {
+            base.LoadComplete();
 
             SkinSources.BindCollectionChanged(((_, args) =>
             {