(assert-typecheck-fail ...) fails with runtime error

A repro:

```racket
#lang typed/racket/base

(: f11 (-> (Listof Real) (Listof Real)))
(define (f11 rs)
  (map (lambda (z) (assert-typecheck-fail (+ z 5.0) #:result (error 'a))) rs))
```

```
../../Applications/Racket9.0/share/pkgs/typed-racket-lib/typed-racket/types/tc-result.rkt:226:2: match: no matching clause for #f
```