Make hwaccel check a bit more robust
If there is a hard coded DISPLAY environment variable, we'll fail to log in to a Wayland session, as the hardware acceleration check will fail. For a Wayland session, gnome-session shouldn't run that check, and did so by checking the DISPLAY environment variable's existance. Change this to first check the XDG_SESSION_TYPE variable, and if it's set to "wayland", also don't do the check. That should mitigate a hard coded DISPLAY being set, at least for system using systemd.