fix: be able to upload files w/o extension

[sam80180]

Whether this PR is eventually merged or not, Sonic will thank you very much for your contribution.

无论此PR最终是否合并，Sonic组织都非常感谢您的贡献。

Checklist

• The title starts with fix, fea, or doc. | 标题为fix、feat或doc开头。
• I have checked that there are no duplicate pull requests with this request. | 我已检查没有与此请求重复的拉取请求。
• I have considered and confirmed that this submission is valuable to others. | 我已经考虑过，并确认这份呈件对其他人很有价值。
• I accept that this submission may not be used. | 我接受此提交可能不会被使用。

Description

If files without extension are uploaded, they cannot be downloaded. The returned download URL is like 'http://xxx:3000/xxx/xxx/null'

[ZhouYixun]

mg