Avoid a 1 byte overcopy in x509_get_subject (ssl_verify_openssl.c)

Avoid a 1 byte overcopy in x509_get_subject (ssl_verify_openssl.c)

This is the equivalent of the 2.3 patch (04c84548c2) by Guido Vranken,
adjusted to code in the master and release/2.4 branches.

Trac: #890

Signed-off-by: Steffan Karger <steffan@karger.me>
Acked-by: Gert Doering <gert@greenie.muc.de>
Message-Id: <143540d4-e8ea-b533-ad1a-8ae33bfd1133@karger.me>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg14653.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>
(cherry picked from commit 3fbc9d2b1b1e75b227107057b92ce6b786b5bea1)