Only take note of the ack deadline if we can actually issue an ack

When determining the next tick deadline we cannot actually issue an
ack if the CC will not let us, or the enc_level is not yet provisioned.

This avoids a bug where we can end up in a busy loop because the next
event deadline is reported as "now" because we want to send an ack, but
we can't actually send anything yet.

Reviewed-by: Tomas Mraz <tomas@openssl.org>
Reviewed-by: Hugo Landau <hlandau@openssl.org>
Reviewed-by: Paul Dale <pauli@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/21181)
