Bug#980061: caribou: Segfault as regression of xorg CVE-2020-25712 fix that cause security issue for cinnamon

[Fabio Fantoni]

Prepared a MR:
https://salsa.debian.org/gnome-team/caribou/-/merge_requests/2

Already tested build
(http://debomatic-amd64.debian.net/distribution#unstable/caribou/0.4.21-7.1~/buildlog
<http://debomatic-amd64.debian.net/distribution#unstable/caribou/0.4.21-7.1~/buildlog>),
installed and verified that issue is not reproducible anymore