Fix io slector unregister for windows as well.

lib/pure/ioselects/ioselectors_select.nim

@@ -286,7 +286,7 @@ proc unregister*[T](s: Selector[T], fd: SocketHandle|int) =
   s.withSelectLock():
     let fd = fd.SocketHandle
     var pkey = s.getKey(fd)
-    if Event.Read in pkey.events:
+    if pkey.events * {Event.Read, Event.User} != {}:
       IOFD_CLR(fd, addr s.rSet)
       dec(s.count)
     if Event.Write in pkey.events: