Incorrect "explicit lifetime name needed" error

```rust
struct Nested<K>(K);

trait X<'a, K: 'a> {
    fn foo<'b, L: X<&'b Nested<K>>>();
}
```
produces:
```
error[E0637]: `&` without an explicit lifetime name cannot be used here
 --> src/lib.rs:4:19
  |
4 |     fn foo<'b, L: X<&'b Nested<K>>>();
  |                   ^^^^^^^^^^^^^^^^ explicit lifetime name needed here
```
despite there being no unnamed `&`.