modesetting: unflip not possible when glamor is not set

This is fixing crashes of xfce when running under qemu
3 jobs for issue1195_fix_on_1.20_branch in 5 minutes and 23 seconds (queued for 6 seconds)
Status Name Job ID Coverage
  Docker Image
passed debian-testing #12299966

00:00:22

 
  Build And Test
passed autotools-build-and-test #12299967

00:05:00

passed meson-build-and-test #12299968

00:01:37