[pty] Return enqueued data and then EIO if the replica is closed

PiperOrigin-RevId: 532496868

pkg/sentry/fsimpl/devpts/queue.go

@@ -110,6 +110,9 @@ func (q *queue) read(ctx context.Context, dst usermem.IOSequence, l *lineDiscipl
 	defer q.mu.Unlock()
 
 	if !q.readable {
+		if l.numReplicas == 0 {
+			return 0, false, false, linuxerr.EIO
+		}
 		return 0, false, false, linuxerr.ErrWouldBlock
 	}