Attempt to match number of template arguments to prune references for unresolved lookup expressions

In the following code

```cpp
template <typename T>
void f() {}

template <typename T, typename U>
void f() {}

template <typename T>
void g() { f<T>(); }
```

Here, even though `f` is unresolved, it cannot match the second case because `U` doesn't have a default value.