refine assertion to allow other modes than CBC

cipher_ctx_final() only returns an outlen in CBC mode. If CFB or OFB
are used the assertion outlen == iv_len is always false.

There's no CBC mode defined for the GOST 28147-89 block cipher. Hence
this patch is needed for it to work. It's needed for other ciphers like
BF-CFB as well, though.

Signed-off-by: Heiko Hund <heiko.hund@sophos.com>
Acked-by: Steffan Karger <steffan.karger@fox-it.com>
Message-Id: <538A00AA.7090007@karger.me>
URL: http://article.gmane.org/gmane.network.openvpn.devel/8748
Signed-off-by: Gert Doering <gert@greenie.muc.de>