Attachement filename is ignored[2023July03]

I've searched #330 , didn't resovled my question.

Attachement filename is still ignored, because in my case the attachment file name is not described in the Content-Type but Content-Disposition.

```
Content-Type: application/octet-stream
MIME-Version: 1.0
Content-Transfer-Encoding: base64
Content-Disposition: attachment; filename*=utf-8''2023%E5%B9%B406%E6%9C%8830%E6%97%A515%E6%97%B610%E5%88%86.zip
```

Thanks for your work.

Start by reproducing the attachment case using the Content-Type and Content-Disposition headers shown in the issue, then trace how attachment filenames are selected. Done means the UTF-8 filename in Content-Disposition, including filename*, is recognized when Content-Type does not describe a filename.

Written by the indexing model from the issue text.