fix(selection.js): getSelectedRows will work on primitive data types.

Ensuring that the presence of $$hashKey is only needed for non-objects.

fix #6704

src/features/selection/js/selection.js

@@ -292,7 +292,7 @@
                   return service.getSelectedRows(grid).map(function (gridRow) {
                     return gridRow.entity;
                   }).filter(function (entity) {
-                    return entity.hasOwnProperty('$$hashKey');
+                    return entity.hasOwnProperty('$$hashKey') || !angular.isObject(entity);
                   });
                 },
                 /**