Fix segfault when handling ECDSA keys
Import patch by Marc Deslauriers from the Ubuntu package of pam_ssh_agent_auth
Ref: https://github.com/jbeverly/pam_ssh_agent_auth/pull/24/files
https://github.com/jbeverly/pam_ssh_agent_auth/issues/18 https://bugs.launchpad.net/ubuntu/+source/pam-ssh-agent-auth/+bug/1869512
PR: 253693
Submitted by: Matt <opensource mtcoster.net>
Obtained from: Marc Deslauriers <marc.deslauriers canonical.com>, Ubuntu