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)
Status Job ID Name Coverage
  Docker Image
passed #3483920
debian-testing

00:00:18

 
  Build And Test
passed #3483921
autotools

00:06:09

passed #3483922
meson

00:02:18

passed #3483923
meson-noglamor

00:00:55