[session-lock] Screenlocker partially drawn over compositor

[travankor]

Describe the bug
The screen locker does not completely draw over the compositor in some cases. The screenlocker still prevents interacting with wayfire, but the contents of the desktop are mostly visible. Tested with swaylock and waylock.

To Reproduce
Steps to reproduce the behavior:

1. sudo runuser -l travankor -c 'WAYLAND_DISPLAY=wayland-1 XDG_RUNTIME_DIR=/run/user/1000 swaylock'

Expected behavior
Screenlocker draws over the whole compositor, like in labwc or sway.

Wayfire version
0.9.0