[release-2.3] fix: the issue of blank content when opening a saved post in StackEdit editor plugin for editing (#905)

This is an automated cherry-pick of #903

/assign JohnNiang

```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 () => {