Oscillator fixes for older Safari browsers

[RazorDE]

2 fixes in 1:

• In some older Safari browsers the parameter for the oscillator's stop/noteOff-function is mandatory (if this isn't set an error occurs and the oscillator won't stop). So I set it to 0 which is the default case in other browsers.
• Some older Safari browsers have a noteOff- instead of a stop-function for the oscillator (similar to the noteOn-case which is already implemented). I've added this and use a tenary operator to select the right function instead of copying it.

[a1k0n]

Nice, thanks!