Fix NPE in backchannel logout

fix #108

 src/main/java/org/keycloak/protocol/cas/CASLoginProtocol.java

@@ -140,8 +140,7 @@
            sendSingleLogoutRequest(logoutUrl, serviceTicket);
        }
        ClientModel client = clientSession.getClient();
        new ResourceAdminManager(session).logoutClientSession(realm, client, clientSession).close();
        return Response.ok().build();
        return new ResourceAdminManager(session).logoutClientSession(realm, client, clientSession);
    }

    private void sendSingleLogoutRequest(String logoutUrl, String serviceTicket) {