unsafe-poller: fix result handling

Closes #2754

pkgs/racket-test-core/tests/racket/sync.rktl

@@ -1005,6 +1005,15 @@
                               (values #f self)]))))
   (test #t sync (p)))
 
+(let ()
+  (struct not-ever-evt ()
+    #:property prop:evt
+    (unsafe-poller
+     (lambda (self wakeups)
+       (printf "~s\n" wakeups)
+       (values #f never-evt))))
+  (test #f sync/timeout 0 (not-ever-evt)))
+
 ;; ----------------------------------------
 ;;  Garbage collection
 

racket/src/racket/src/struct.c

@@ -1661,7 +1661,7 @@ static int evt_struct_is_ready(Scheme_Object *o, Scheme_Schedule_Info *sinfo)
           v = scheme_make_closed_prim_w_arity(return_wrapped, (void *)v, "wrapper", 1, 1);
       }
       scheme_set_sync_target(sinfo, v, (done ? v : NULL), NULL, 0, 0, NULL);
-      return 1;
+      return done;
     }
   }