Fix "audio used before assigned" bug (#2898)
* Fix "audio used before assigned" bug
audio_from_file did not correctly handle the case where the file cannot be opened. This PR fixes e.g. the crash mentioned in [TheAlly's Riffusion tutorial](https://theally.notion.site/theally/Quick-n-Dirty-Riffusion-txt2audio-Tutorial-18e57df9ef214c3280efc5998bbf774d).
* Update CHANGELOG.md
* Output helpful message about ffprobe
* Output error message
* Raise chained RuntimeError with full description
* Fix indentation
* Fixed spacing
Co-authored-by: Freddy Boulton <alfonsoboulton@gmail.com>
