_playInstance parameters affectation fix

plus the fact it is a very bad programming habit affecting function parameters in Sound._playInstance simply is dodgy. 

Found this after multiple testing where my Sound.play("file",{loop:-1}) parameter was not taken into account and no looping was happening. For now I'm using the old fashion parameters list cause the affectation result is very random. Some parameters are ok, others are not depending on Idontreallyknowwhat JS engine black magic ;).