typeintersect bug with NTuple

```julia
julia> typeintersect((Tuple{Vararg{Union{},A}} where A), Tuple{Int64, Vararg{Int64, N} where N}) !== Union{}
false
```

This is bad since the intersection is non-empty when `A` is later given:
```julia
julia> typeintersect((Tuple{Vararg{Union{},3}} where A), Tuple{Int64, Vararg{Int64, N} where N}) !== Union{}
true
```