Handle a couple of NULL QUIC ctx.qc values

Handle a couple of NULL QUIC ctx.qc values

Now that we also QUIC server (listener) handles, we may have a NULL quic
connection (ctx.qc), and so need to either return early or handle the
NULL `qc` gracefully.

Reviewed-by: Sasa Nedvedicky <sashan@openssl.org>
Reviewed-by: Matt Caswell <matt@openssl.org>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/25432)