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 master in 3 minutes and 43 seconds (queued for 1 second)
Status Job ID Name Coverage
  Docker Image
passed #3483986
debian-testing

00:00:17

 
  Build And Test
passed #3483987
autotools

00:03:26

passed #3483988
meson

00:01:03

passed #3483989
meson-noglamor

00:00:51