Guard against nil session in consent confirmation notifier

Old unmatched consent forms can have a `ni`l session if the original session was deleted, causing a `NoMethodError` when attempting to send the confirmation email.
We’ve only just encountered these errors (in `test` and `qa`) as we recently introduced the processing of unmatched consents daily, which touches on very old consent forms too.

Author: murugapl

app/lib/notifier/consent_form.rb

@@ -62,7 +62,7 @@ def send_confirmation_given(programme_types: nil, disease_types: nil)
 
     if consent_form.health_answers_require_triage?
       EmailDeliveryJob.perform_later(:consent_confirmation_triage, **params)
-    elsif consent_form.session.clinic? || consent_form.session.completed?
+    elsif consent_form.session&.clinic? || consent_form.session&.completed?
       EmailDeliveryJob.perform_later(:consent_confirmation_clinic, **params)
     else
       EmailDeliveryJob.perform_later(:consent_confirmation_given, **params)