Fix a bug with AudioBufferSourceNode 
Fix a bug with AudioBufferSourceNode 

https://github.com/goldfire/howler.js/issues/226

It seems as though AudioBufferSourceNode can get caught in cases where the seek and duration are negative 
"Failed to execute 'start' on 'AudioBufferSourceNode': The duration provided (-0.17) is less than the minimum bound (0)"

We can protect this by defaulting to 0 when we seek or set a duration below 0.
goldfire/howler.js,goldfire/howler.js