record the correct pid for ibus-daemon

[totaam]

We run:

xpra/xpra/scripts/server.py

Lines 64 to 65 in 7a77df6

	IBUS_DAEMON_COMMAND = os.environ.get("XPRA_IBUS_DAEMON_COMMAND",
	"ibus-daemon --xim --verbose --replace --panel=disable --desktop=xpra --daemonize")

And we then record the pid, expecting to be able to use it later:

xpra/xpra/scripts/server.py

Lines 1087 to 1091 in 7a77df6

	# maybe we are inheriting one from a dead session?
	ibus_daemon_pid = load_pid(session_dir, "ibus-daemon.pid")
	if not ibus_daemon_pid or not os.path.exists("/proc") or not os.path.exists(f"/proc/{ibus_daemon_pid}"):
	Logger("ibus").debug("adding ibus-daemon to late startup")
	opts.start_late.insert(0, IBUS_DAEMON_COMMAND)

This cannot work since the process has daemonized and therefore changed its pid.
We could handle the daemonization ourselves and return the correct pid:

xpra/xpra/server/util.py

Lines 334 to 340 in 7a77df6

	def daemonize() -> None:
	os.chdir("/")
	if os.fork():
	os._exit(0) # pylint: disable=protected-access
	os.setsid()
	if os.fork():
	os._exit(0) # pylint: disable=protected-access

First reported in #4449 (comment)