Validate RE2 instance before unwrapping

[theosotr]

fixes #285

[uhop]

Thank you for the report and the fix!

I reproduced it: on Node 26 new RE2(new RE2.Set(['abc'])) segfaults, and so does any other natively wrapped object, like a MessagePort or a v8.Serializer. Your change is the right one: WrappedRE2::HasInstance() is how the rest of the addon already checks its receivers, and this was the one place that relied on InternalFieldCount().

For the record, I treat this as a usage error, not a vulnerability. The TypeScript definitions reject new RE2(set) (TS2769), so a modern IDE flags it before it runs. Still, an answer to a wrong argument should be a TypeError not a crash.

I'm merging it as is. I'll add regression tests separately, and the fix will go out with the next release.