ItemsModel3D [UWP] doesn't implement ItemTemplateSelector

[SnowyWreath]

In the methods OnItemsSourceChanged and ItemsModel3D_CollectionChanged in the ItemsModel3D class, there is a check for an item template, but then no check for an ItemTemplateSelector before trying to use the item directly. However, the ItemTemplateSelector dependency property is available. Using it results in an InvalidOperationException because ItemTemplate is null but the items are not Element3D objects.