Handle connecting clients without NCP or OCC without crashing.

Handle connecting clients without NCP or OCC without crashing.

ssl_ncp.c:ncp_get_best_cipher() would crash if a client connects without
NCP (or with a NCP cipher list that does not contain the first NCP cipher
in the server list) due to a NULL pointer strcmp().

Work around / fix by just assigning an empty string to remote_cipher here
("not NULL but will never match either").

Add new warning message in multi.c for the "we do not know what the
client can do" case (no NCP and non-helpful OCC), rewrapped the existing
message to keep line lenght limit.

Signed-off-by: Gert Doering <gert@greenie.muc.de>
Acked-by: Arne Schwabe <arne@rfc2549.org>
Message-Id: <20200713093252.30916-1-gert@greenie.muc.de>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg20309.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>