[XWayland] Portions of window get painted with solid white color

To reproduce: on a Linux desktop running Wayland (like Ubuntu 22.04 or Fedora 36) compile and run the attached program. It may need a few times for the bug to show up as a vertical white rectangle instead of a grey rectangle with rounded corners (see attached "good" and "bad" screenshots).

Workarounds:
* Disable Glamor (set XWAYLAND_NO_GLAMOR=1 in /etc/environment, then reboot the system).
* Change the default Java graphics pipeline to OpenGL: run java with -Dsun.java2d.opengl=true