xwayland: Fix a couple of file descriptor leaks
The -wm file descriptor leak prevents the poll() function from returning POLLHUP when Xwayland dies.
The POLLHUP status will be set when all file descriptors for the other end point are closed.
(cherry picked from commit 40d20297)
Co-authored-by: Vlad Zahorodnii vlad.zahorodnii@kde.org