fix return_type_tfunc in the case where no methods match

[JeffBezanson]

I discovered this while working on #20033. Example:

julia> Base.Broadcast._broadcast_eltype(g.f, g.iter)
Union{}

julia> @code_typed Base.Broadcast._broadcast_eltype(g.f, g.iter)
CodeInfo(:(begin 
        return $(QuoteNode(Any))
    end))=>Type{Any}

Changing map to match broadcast will require this bugfix, but will be a separate change.

[martinholters]

Would we still need the "no methods match" part of this if we chose to merge #20866? (Just curiosity; I'm not implying we should prefer #20866 over this one.)

[tkelman]

doesn't necessarily... what, do the same?

[tkelman]

this isn't all that clear and seems incomplete ending in an adverb

[JeffBezanson]

#20866 would definitely simplify this, it just seems riskier. It would also be better for return_type to call abstract_call, so there is less opportunity for it to diverge from other inference code.