Completion for type parameters doesn't work when used as first type argument of type reference in a TSX file

Given any of the following:

``` TypeScript
interface I<T1,T2> {
    next: I</*interface*/
}

type T<T1,T2> = {
    next</*typeAlias*/
}

class C<T1,T2> {
    next: C</*class*/
}
```

we do not give completion for `T1` nor `T2`. However, if you add a comma following at least one type argument, you do get both `T1` and T2` for the next type argument.
