Save the first non-empty line as recipient

Since we now allow the address to be populated from any three lines, we
can’t guarantee that the recipient will be in the `addressline1` field.

app/celery/tasks.py

@@ -3,6 +3,8 @@ from datetime import datetime
 from collections import namedtuple, defaultdict
 
 from flask import current_app
+from notifications_utils.columns import Columns
+from notifications_utils.postal_address import PostalAddress
 from notifications_utils.recipients import RecipientCSV
 from notifications_utils.statsd_decorators import statsd
 from notifications_utils.timezones import convert_utc_to_bst
@@ -341,7 +343,9 @@ def save_letter(
     notification = encryption.decrypt(encrypted_notification)
 
     # we store the recipient as just the first item of the person's address
-    recipient = notification['personalisation']['addressline1']
+    recipient = PostalAddress.from_personalisation(
+        Columns(notification['personalisation'])
+    ).normalised_lines[0]
 
     service = dao_fetch_service_by_id(service_id)
     template = dao_get_template_by_id(notification['template'], version=notification['template_version'])