fix: selector

src/Std/Internal/Async/Signal.lean

@@ -244,19 +244,22 @@ does not start the signal waiter.
 def selector (s : Signal.Waiter) : Selector Unit :=
   {
     tryFn := do
-      let signalWaiter : AsyncTask _ ← async s.wait
-      if ← IO.hasFinished signalWaiter then
+      let signalWaiter ← s.native.next
+      if ← signalWaiter.isResolved then
         return some ()
       else
         s.native.cancel
         return none
 
     registerFn waiter := do
-      let signalWaiter ← s.wait
-      discard <| AsyncTask.mapIO (x := signalWaiter) fun _ => do
-        let lose := return ()
-        let win promise := promise.resolve (.ok ())
-        waiter.race lose win
+      let signalWaiter ← s.native.next
+      BaseIO.chainTask signalWaiter.result? fun
+        | none => do
+          return ()
+        | some _ =>
+          let lose := return ()
+          let win promise := promise.resolve (.ok ())
+          waiter.race lose win
 
     unregisterFn := s.native.cancel