[BUG] WriteToFile fails to create backup file before overwriting existing content

[sakura-3]

BUG REPORT

1. Please describe the issue you observed:

   • What did you do (The steps to reproduce)?
     尝试向一个已存在的非空文件写入内容。

   • What did you expect to see?
     内容成功写入指定位置，原文件内容写入到备份文件中。

   • What did you see instead?
     备份文件内容为空

2. Please tell us about your environment:

3. Other information (e.g. detailed explanation, logs, related issues, suggestions on how to fix, etc):
   应该是err==nil 时写入

[sakura-3]

对应的PR: #1199