[acorn-optimizer] unsignPointers can cause problems optional second argument `subarray`

[sbc100]

The unsignPointers pass will currently add >>> 0 to all arguments to \.subarray.

However, if the value being passed is undefined this changes its meaning.

The case I found was in library_glemu.js which does something like this: HEAP16.subarray(ptr, end ? end : undefined).

In the case when end is undefined this ends up being end >>> 0 which is 0, and which is very different to undefined when passed as this argument.