core: Fix some corrupted audio by preventing negative volume

[iscwDu]

Fixes #16234

I'm not a rust programmer, if there is a more idiomatic way to do this, please let me know. Thanks! (Edit: I did compile and run this against SDT to confirm that it fixes the audio issues, with and without '--release' )

I also wasn't sure if negative volumes should be clipped to zero or just treated as positive. This makes more sense to me as it looks like they could arise when doing some weird audio panning.

[kjarosh]

Can you add a test for it? See for details:

1. https://github.com/ruffle-rs/ruffle/blob/master/CONTRIBUTING.md#test-guidelines
2. https://github.com/ruffle-rs/ruffle/blob/master/tests/README.md

We'd probably need a test that sets negative volume and then reads it back and plays audio. Then we can verify if the audio is playing. This way you'll know whether that's the right place to fix it and whether you should clamp it or abs it.