Fix crash when a record union contains any()

[erszcz]

Fixes #445.

[zuiderkwast]

Looks like this will solve the issue. I have some suggestion but you can choose which solution you prefer.

There is some redundant code here. What if expect_record_type could return fields_tys in more cases, e.g. in the case of no union (a single record type) and in the case of any as well, could that get rid of some duplication? (optional)

[erszcz]

There is some redundant code here. What if expect_record_type could return fields_tys in more cases, e.g. in the case of no union (a single record type) and in the case of any as well, could that get rid of some duplication? (optional)

Good point, we can simplify it all a bit. I'll make this change before we merge this.

[erszcz]

There is some redundant code here. What if expect_record_type could return fields_tys in more cases [...]

Ok, I did give it a try, but it's no use. Whatever we gain in do_type_check_expr_in we lose in add_type_pat, which is another call site of expect_record_type, but unions are handled completely differently there so reusing their code path doesn't make sense.

Why not add a clause in type_check_record_union_in?

But I did that, so there's a tiny bit less repetition :)