write metadata artist to ? maybe encoding error

**Describe the bug**
command
```
./ffmpeg -i 002.mp3 -c copy -metadata:s:a title="暧昧" -metadata:s:a album="菲主打" -metadata artist="王菲" tmp-3.mp3
```

this command works well with ffmpeg binary from ffmpeg.org, but get result like this with ffmpeg.wasm
```
Metadata:
title : 暧昧
album : 菲主打
artist : ??
```

any mp3 file can reproduce