Fix use-after-free in xenconsoled.

Fix use-after-free in xenconsoled.

shutdown_domain() MUST NOT call cleanup_domain(), just flagging them
as dead is enough.  cleanup_domains() for dead domains is called by
the main loop in handle_io() in a safe way already.

shutdown_domain() calling cleanup_domain() too leads struct domain
being accessed after freeing and to a double-free.

Fixed by simply dropping the cleanup_domain() call and by making the
functions called by the main loop in handle_io() ignore dead domains.

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>