fix (-> any/c boolean?) for the case of an impersonated struct predicate

closes #1129

pkgs/racket-test/tests/racket/contract/arrow.rkt

@@ -386,6 +386,13 @@
   (test/pos-blame
    'predicate/c13
    '(contract (-> any/c boolean?) (λ (x #:y y) #t) 'pos 'neg))
+  (test/pos-blame
+   'predicate/c14
+   '(contract (-> any/c boolean?)
+              (let ()
+                (struct s ())
+                ((impersonate-procedure s? (λ (x) (values (λ (r) "") x))) 11))
+              'pos 'neg))
   
   ;; this test ensures that no contract wrappers
   ;; are created for struct predicates

racket/collects/racket/contract/private/arrow-val-first.rkt

@@ -1289,7 +1289,9 @@
                                 given: "~e")
                     f))
                  (cond
-                   [(struct-predicate-procedure? f) #f]
+                   [(and (struct-predicate-procedure? f)
+                         (not (impersonator? f)))
+                    #f]
                    [(and (equal? (procedure-arity f) 1)
                          (let-values ([(required mandatory) (procedure-keywords f)])
                            (and (null? required)