Fix forced-layout example trigger insert untitle node (#5263)

Co-authored-by: 锐雯 <wangyichen@xiaohongshu.com>

site/examples/forced-layout.tsx

@@ -6,6 +6,7 @@ import {
   Node,
   Element as SlateElement,
   Descendant,
+  Editor,
 } from 'slate'
 import { withHistory } from 'slate-history'
 import { ParagraphElement, TitleElement } from './custom-types'
@@ -15,12 +16,15 @@ const withLayout = editor => {
 
   editor.normalizeNode = ([node, path]) => {
     if (path.length === 0) {
-      if (editor.children.length < 1) {
+      if (editor.children.length <= 1 && Editor.string(editor, [0, 0]) === '') {
         const title: TitleElement = {
           type: 'title',
           children: [{ text: 'Untitled' }],
         }
-        Transforms.insertNodes(editor, title, { at: path.concat(0) })
+        Transforms.insertNodes(editor, title, {
+          at: path.concat(0),
+          select: true,
+        })
       }
 
       if (editor.children.length < 2) {