HTTP uploads with `curl` fail silently or with a 400

When uploading a file with the following command:
```bash
curl -T ./document.pdf https://transit.sh/my-file/ --expect100-timeout 300
```

Either:
- A 400 response is returned with the message "Invalid metadata".
- The uploads fails silently server-side


**I'm working on the issue and will push a fix soon!**