Do not check key_state buffers that are in S_UNDEF state

Do not check key_state buffers that are in S_UNDEF state

When a key_state is in S_UNDEF the send_reliable is not initialised. So
checking it might access invalid memory or null pointers.

Github: fixes OpenVPN/openvpn#449

Change-Id: I226a73d47a2b1b29f7ec175ce23a806593abc2ac
[a@unstable.cc: add check for !send_reliable and message]
Signed-off-by: Arne Schwabe <arne@rfc2549.org>
Acked-by: Gert Doering <gert@greenie.muc.de>
Message-Id: <20231115103331.18050-1-gert@greenie.muc.de>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg27401.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>
(cherry picked from commit a903ebe9361d451daee71c225e141f4e1b67107d)