[Layout] Fix comment

Change inaccurate comment based on feedback from code
review for WTD-1182.

platform/features/layout/src/LayoutController.js

@@ -69,7 +69,8 @@ define(
             function lookupPanels(ids) {
                 var configuration = $scope.configuration || {};
 
-                // Ensure ids is array-like
+                // ids is read from model.composition and may be undefined;
+                // fall back to an array if that occurs
                 ids = ids || [];
 
                 // Pull panel positions from configuration