tests/qapi-schema: Cover 'Features:' not followed by descriptions

A 'Features:' line without any features is useless, but not an error
now.  However, a later commit will make it one, because that makes
rejecting duplicate 'Features:' easier.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Message-ID: <20240216145841.2099240-4-armbru@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
4 files changed