QSslCertificate::verify does not find any roots when on-demand loading is used

QSslSocket::verify uses defaultCaCertificates() to populate the certificate
store with root certificates. However, when
QSslSocketPrivate::ensureCiphersAndCertsLoaded() decides that on-demand loading
of roots is possible, defaultCaCertificates() returns an empty list.

As a result, QSslSocket::verify will fail since it
doesn't use the same roots as a regular SSL connection handshake.

QSslSocket::verify should probably use the same method as
QSslSocketBackendPrivate::initSslContext:

    if (s_loadRootCertsOnDemand && allowRootCertOnDemandLoading) {
        // tell OpenSSL the directories where to look up the root certs on
demand
        QList<QByteArray> unixDirs = unixRootCertDirectories();
        for (int a = 0; a < unixDirs.count(); ++a)
            q_SSL_CTX_load_verify_locations(ctx, 0,
unixDirs.at(a).constData());
    }

Attached example to reproduce.