Parser.MP3: Fix frame size calculation
Parser.MP3: Fix frame size calculation

Tracking down an issue @scrudge saw in #40. Ended up finding the solution
here:

http://www.hydrogenaud.io/forums/index.php?showtopic=85125

pteich/StreamMachine,StreamMachine/StreamMachine,pedropapa/StreamMachine,pteich/StreamMachine,pedropapa/StreamMachine,cdgraff/StreamMachine,SCPR/StreamMachine,cdgraff/StreamMachine,SCPR/StreamMachine,StreamMachine/StreamMachine