Make alert page work for rejected broadcasts

The code for this page was making assumptions about properties which
aren’t present on rejected broadcasts.

This commit accounts for those properties and presents the relevant
elements on the page.

app/models/broadcast_message.py

@@ -158,7 +158,7 @@ class BroadcastMessage(JSONModel):
 
     @cached_property
     def approved_by(self):
-        return User.from_id(self.approved_by_id)
+        return User.from_id(self.approved_by_id) if self.approved_by_id else None
 
     @cached_property
     def cancelled_by(self):

app/templates/views/broadcast/view-message.html

@@ -116,6 +116,11 @@
           <a href="{{ url_for('.cancel_broadcast_message', service_id=current_service.id, broadcast_message_id=broadcast_message.id) }}" class="destructive-link destructive-link--no-visited-state">Stop broadcasting</a>
         {% endif %}
       </p>
+    {% elif broadcast_message.status == 'rejected' %}
+      <p class="govuk-body govuk-!-margin-bottom-4">
+        Rejected
+        {{ broadcast_message.updated_at|format_datetime_human }}.
+      </p>
     {% else %}
       <p class="govuk-body govuk-!-margin-bottom-4">
         Broadcast
@@ -150,10 +155,13 @@
     <p class="govuk-body govuk-!-margin-bottom-3">
       {% if broadcast_message.created_by %}
         Prepared by {{ broadcast_message.created_by.name }}
-      {% else %}
+      {%- else %}
         Created from an API call
-      {% endif %}
-      and approved by {{ broadcast_message.approved_by.name }}.
+      {%- endif %}
+      {%- if broadcast_message.approved_by %}
+        and approved by {{ broadcast_message.approved_by.name }}
+      {%- endif %}
+      {{- '.' }}
     </p>
   {% endif %}