BUG/MAJOR: ssl/ocsp: fix NULL conn object dereferencing to access QUIC TLS counters

BUG/MAJOR: ssl/ocsp: fix NULL conn object dereferencing to access QUIC TLS counters

This bug arrived with this commit in the current dev branch:

	056ec51c26 MEDIUM: ssl/ocsp: counters for OCSP stapling

and could occur for QUIC connections during handshake when the underlying
<conn> connection object is not already initialized. So in this case the TLS
counters attached to TLS listeners cannot be accessed through this object but
from the QUIC connection object.

Modify the code to initialize the listener (<li> variable) for both QUIC
and TCP connections, then initialize the variables for the TLS counters
if the listener is also initialized.

Thank you to @Tristan971 for having reported this issue in GH #2833.

Must be backported with the commit mentioned above if it is planned to be
backported.