Log Message:
modular-xorg-xephyr: fix Xephyr visual with -parent option

This patch was imported from
https://gitlab.freedesktop.org/xorg/xserver/-/issues/128.

It notably fixes embedding Xephyr into Gtk+ 3 applications, such as
simulator(1) from devel/deforaos-coder.

Tested on netbsd-9/amd64.