Resolve panics happening on handling SSH connection by gitlab-sshd

Return metadata context without using channels (!810 - merged) was supposed to fix the panic. It did but introduced another one.

When handle function is not called, the context is never assigned. It causes a nil pointer error here.

As an improvement, we need to log error. It would simplify the investigation: https://nonprod-log.gitlab.net/app/r/s/dmvW5