ssl_tls: avoid the appearance of a potential NULL dereferencing

[leorosen]

Looking at the bigger picture it is clear that if ssl->session is NULL, there will be a failure much earlier, and that is well protected from, however, the practice of dereferencing a pointer which has not been verified in prior for validity goes against secure coding practices.

Description

See #6183

Status

READY

Requires Backporting

NO

Migrations

NO