fix: the issue of blank content when opening a saved post in StackEdit editor plugin for editing (#903)

> **Warning**
>
> 此 PR 的改动来自：<https://github.com/halo-dev/halo/pull/3468>
> 因为目前 Console 仓库已经合并到 Halo 主仓库，但主仓库的 release-2.3 分支不包含 Console，所以如果需要发布 2.3.x 的 patch 版本，依旧需要在此仓库修改。

#### What type of PR is this?

/kind bug
/milestone 2.3.2

#### What this PR does / why we need it:

在编辑器初始化前赋值，可以保证缓存的历史数据附在StackEdit的url上。

#### Which issue(s) this PR fixes:

Fixes (https://github.com/halo-dev/halo/issues/3105)

#### Screenshots:
![test](https://user-images.githubusercontent.com/88016243/222957520-b7980ff9-aeeb-4e98-9dde-50eb307f02eb.gif)

#### Special notes for your reviewer:

+ 新建文章，切换为 StackEdit 编辑器
+ 输入一些内容保存/发布文章
+ 回到文章列表，重新点进刚才的文章
+ 重复步骤3，输入的内容还在

#### Does this PR introduce a user-facing change?


```release-note
修复 Console 端在使用三方编辑器插件编辑文章时可能出现无法加载内容的问题。
```

src/modules/contents/pages/SinglePageEditor.vue

@@ -208,6 +208,8 @@ const handleFetchContent = async () => {
     name: formState.value.page.metadata.name,
   });
 
+  formState.value.content = Object.assign(formState.value.content, data);
+
   // get editor provider
   if (!currentEditorProvider.value) {
     const preferredEditor = editorProviders.value.find(
@@ -249,8 +251,6 @@ const handleFetchContent = async () => {
     }
     await nextTick();
   }
-
-  formState.value.content = Object.assign(formState.value.content, data);
 };
 
 // SinglePage settings

src/modules/contents/posts/PostEditor.vue

@@ -213,6 +213,8 @@ const handleFetchContent = async () => {
     name: formState.value.post.metadata.name,
   });
 
+  formState.value.content = Object.assign(formState.value.content, data);
+
   // get editor provider
   if (!currentEditorProvider.value) {
     const preferredEditor = editorProviders.value.find(
@@ -256,8 +258,6 @@ const handleFetchContent = async () => {
 
     await nextTick();
   }
-
-  formState.value.content = Object.assign(formState.value.content, data);
 };
 
 const handleOpenSettingModal = async () => {