Fix uglify:generated task when no html exists in the site.

@@ -343,6 +343,8 @@ module.exports = function (grunt) {
         if (mpConfig.uglify) {
         if (mpConfig.uglify) {
             initConfig.uglify = {
             initConfig.uglify = {
                 options: mpConfig.uglify,
                 options: mpConfig.uglify,
+                generated: {
+                },
             };
             };
         }
         }