fix(使所有主题的404能够正常运转)

(cherry picked from commit 3e3b7667d043522a3d782b804815b8f1683127d1)

themes/starter/index.js

@@ -159,7 +159,7 @@ const LayoutSlug = props => {
           <div id='container-inner' className='w-full p-4'>
             {lock && <ArticleLock validPassword={validPassword} />}
 
-            {!lock && (
+            {!lock && post && (
               <div id='article-wrapper' className='mx-auto'>
                 <NotionPage {...props} />
                 <Comment frontMatter={post} />