Adjust weak_ref_alive to allow for "undefined" to match VM behavior

[nommiin]

At the moment, passing undefined into weak_ref_alive on HTML5 will cause yyError("incorrect number of arguments to weak_ref_alive"); to be thrown. On VM/YYC, the function will return undefined without error.

This behavior does not match what occurs on VM (and YYC) and what is stated in the documentation:

Note that if you supply a value that is not a weak reference, the function will return undefined.

My PR adjusts weak_ref_alive to instead check if any arguments are provided, rather than checking for undefined. This brings the functionality to match VM and YYC as of beta v2024.1400.0.836

[nommiin]

Checking through the codebase, maybe it makes more sense to check if there's explicitly 1 argument but alas...