Do not recover from `Trait()` if generic list is unterminated If we encounter `fn foo<T: Trait()`, the recovery logic would it as if `Trait` was intended to use the Fn-like trait syntax, but if we don't know for certain that we've parsed a full trait bound (`fn foo<T: Trait()>`), we bail from the recovery as more likely there could have been a missing closing `>` and the `(` corresponds to the start of the fn parameter list. Fix rust-lang/rust#141436.