Fix 1 occurrence of always-throwing-if-to-when

Using `when` and `unless` is simpler than a conditional with an always-throwing branch.

Author: resyntax-ci[bot]

scribble-test/tests/scribble/reader.rkt

@@ -947,14 +947,14 @@ END-OF-TESTS
           (define m
             (or (regexp-match #px"^(.*)\n\\s*(-\\S+->)\\s*\n(.*)$" t)
                 (regexp-match #px"^(.*\\S)\\s+(-\\S+->)\\s+(\\S.*)$" t)))
-          (if (not (and m (= 4 (length m))))
-              (error 'bad-test "~a" t)
-              (let-values ([(x y) ((string->tester (caddr m)) (cadr m) (cadddr m))])
-                (test #:failure-message (format "bad result in\n    ~a\n  results:\n    ~s != ~s"
-                                                (regexp-replace* #rx"\n" t "\n    ")
-                                                x
-                                                y)
-                      (matching? x y)))))))
+          (unless (and m (= 4 (length m)))
+            (error 'bad-test "~a" t))
+          (let-values ([(x y) ((string->tester (caddr m)) (cadr m) (cadddr m))])
+            (test #:failure-message (format "bad result in\n    ~a\n  results:\n    ~s != ~s"
+                                            (regexp-replace* #rx"\n" t "\n    ")
+                                            x
+                                            y)
+                  (matching? x y))))))
 
     ;; Check static versus dynamic readtable for command (dynamic when "c" in the
     ;; name) and datum (dynamic when "d" in the name) parts: