Closure incorrectly tries to move instead of borrow in `ref` patterns within `if let`

[Veykril]

struct NotCopy;
struct S(NotCopy);
impl S {
    fn f(&mut self) {
        || {
            if let ref mut cb = self.0 {
            }
        };
    }
}

This incorrectly reports cannot move NotCopy out of reference. This closure is not actually moving the 0 field out.