CloneModelView: Verify the view is not there before creation to suppo…

…rt special cases, e.g ModelDifference #908

src/Modules/CloneModelView/CloneModelViewService.cs

@@ -68,6 +68,7 @@ static void AssignAsDefaultView(this CloneModelViewAttribute cloneModelViewAttri
 
 		static void GenerateModel(this IModelViews views, IModelClass classInfo){
 			var cloneViewAttributes = classInfo.TypeInfo.FindAttributes<CloneModelViewAttribute>(false)
+				.Where(attribute => views[attribute.ViewId]==null)
 				.OrderBy(viewAttribute => viewAttribute.ViewType);
 			foreach (var cloneViewAttribute in cloneViewAttributes){
 				var modelView = views.NewModelView( cloneViewAttribute, classInfo);