Optimize varargs with js.WrappedArray.

I prefer not to crash because there is a perfectly valid translation (just not as optimized) which is what I do here: map all arguments, and do not optimize repeated params.

Failing to protect ourselves from unexpected cases has cause trouble in the past, for example #599. If we have a valid fallback when trying to optimize stuff rather than doing the stupid translation, we should use the fallback, not crash.