A few commits ago (v10.4.0-101-gc65eba1f57) I've introduced
virDomainDefLaunchSecurityValidate() and a switch() statement in
it. Some cases are empty but are lacking 'break' statement which
is not valid. Provide missing 'break' statement.
Signed-off-by: Michal Privoznik <mprivozn@redhat.com>