Fix SSL client connection crash for SAN marked critical
The patch for CVE-2013-4073 (https://gist.github.com/nahi/5880963) caused SSL crash when a SSL server returns the certificate that has critical SAN value. X509 extension could include 2 or 3 elements in it;
[id, criticality, octet_string] if critical,
[id, octet_string] if not.
Making sure to pick the last element of X509 extension and use it as SAN value.