prevent infinite loop in cleanup code for

io_close-with-outstanding-events-queued race prevention

io/io_waituntil2.c

@@ -123,12 +123,11 @@ int64 io_waituntil2(int64 milliseconds) {
   if (first_deferred!=-1) {
     while (first_deferred!=-1) {
       io_entry* e=iarray_get(&io_fds,first_deferred);
-      if (e) {
+      if (e && e->closed) {
-	if (e->closed) {
 	e->closed=0;
 	close(first_deferred);
-	}
 	first_deferred=e->next_defer;
+	e->next_defer=-1;
       } else
 	first_deferred=-1;	// can't happen
     }