Clamping OggStream.Volume to a min value of 0 to avoid OpenAL errors

During a fade out I set Volume (inadvertently) to a value of -0.09 which caused OpenTK/OpenAL to throw an error. Clamping the value coming in to be no lower than 0 seems a good fix for that.

Apparently my text editor also decided to change some spacing or tabs or something so it looks like a lot more has changed than actually did. :)