[seamlisten] internal server error for some data

Internal server error displayed when trying to diplay file containing mixed format audios:

```
1.2276291 /path/to/mp3/some.mp3 12710400 12744672 223 /path/to//raw_audios/fr/2016/20160926.ogg|2963328|2965566
```

[Internal issue: 21]

Start by reproducing the error with the mixed-format audio line shown in the issue, including both the MP3 and OGG paths. Trace the seamlisten entry point that displays this data and identify where the internal server error is produced. Done means this input displays successfully without an internal server error.

Written by the indexing model from the issue text.