fix #43411, wrapped NamedTuple can be bitstype more often

[JeffBezanson]

fix #43411

[vtjnash]

Seems like jl_get_fieldtypes is sometimes invalid for NamedTuple, as a special case here:

julia/src/jltypes.c

Line 1519 in afd9926

ndt->types = jl_emptysvec; // XXX: this is essentially always false

and we need to avoid using it, as this PR does

But if jl_get_fieldtypes was returning svec() here, how did we end up returning 1 from this function? Ah, I see we were incorrectly returning 0 here earlier, since the fieldtypes we considered were incorrect.

[vtjnash]

Is this comment unnecessary now?

julia/src/jltypes.c

Lines 228 to 229 in afd9926

	if (jl_is_tuple_type(dt) || jl_is_namedtuple_type(dt))
	return 0; // TODO: relax more?