Btw, now that I read the existing library_openal.js code, I think this "minus one" biz is very silly and we should just remove all of those, and always make `AL.currentContext.buf[0] = null;` at initialization time. Or alternatively refactor the whole logic to a `currentContext.getBuffer(id)` function that does the minus one. Having to do this in each place separately is very error-prone and not a good idea.

I understand this is an issue about the existing code, not of your pull request :) so feel free to change whichever way you like, e.g. just locally adding the `bufferId-1` here is ok for the PR as well.