user_has_groups is used to check for groups in e.g. view attributes (`@groups`).
When trying to format lists of groups in views, it would break down as it would
pass e.g. `\n some.group` to `res.users.has_group`, which would look for
an xid with the module `\n some` and (oddly enough) not find it.
Theoretically could also handle that inside res.users.has_group but it seems
ever-so-slightly more risky, and has_group is only used programmatically and
should thus already be called correctly.
fixes#9797