fix use of in-producer outside of for loops

- make-do-sequence was giving producer fn an argument when none was expected

Closes PR 13986

pkgs/racket-pkgs/racket-test/tests/racket/for.rktl

@@ -105,7 +105,9 @@
   (test-sequence [(1 2 3 4)] (for/list ([x (in-producer (counter))] #:break (= x 5)) x))
   (test-sequence [(1 2 3 4)] (for/list ([x (in-producer (counter) 5)]) x))
   (test-sequence [(1/2 1 3/2 2 5/2 3 7/2 4 9/2)]
-    (for/list ([x (in-producer (counter) 5 1/2)]) x)))
+    (for/list ([x (in-producer (counter) 5 1/2)]) x))
+  ;; test in-producer outside of for loops
+  (test 6 sequence-ref (in-producer (counter)) 5))
 
 (test-sequence [(1 2 3 4 5)]
   (parameterize ([current-input-port (open-input-string "1 2 3\n4 5")])

racket/collects/racket/private/for.rkt

@@ -1051,7 +1051,7 @@
     (case-lambda
       [(producer)
        ;; simple stop-less version
-       (make-do-sequence (lambda () (values producer void (void) #f #f #f)))]
+       (make-do-sequence (lambda () (values (λ _ (producer)) void (void) #f #f #f)))]
       [(producer stop . more)
        (define produce!
          (if (null? more)