xwayland: Propagate damage x1/y1 coordinates in xwl_present_flip

This couldn't have worked correctly for non-0 x1/y1.

Noticed by inspection.

Reviewed-by: Simon Ser <contact@emersion.fr>
4 jobs for xwl_present_flip-damage-xy1 in 6 minutes and 27 seconds (queued for 1 second)