Check for suspension before sending a broadcast

This mirrors the check we do for jobs, which are also a high-impact
task [1]. While this shouldn't be possible, just like other checks
we're adding it here to be doubly certain.

[1]: 3d71815956/app/celery/tasks.py (L74)

app/celery/broadcast_message_tasks.py

@@ -56,6 +56,12 @@ def check_provider_message_should_send(broadcast_event, provider):
     4. If you need to re-send this task off again, you'll need to run the following command on paas:
        `send_broadcast_provider_message.apply_async(args=(broadcast_event_id, provider), queue=QueueNames.BROADCASTS)`
     """
+    if not broadcast_event.service.active:
+        raise BroadcastIntegrityError(
+            f'Cannot send broadcast_event {broadcast_event.id} ' +
+            f'to provider {provider}: the service is suspended'
+        )
+
     current_provider_message = broadcast_event.get_provider_message(provider)
     # if this is the first time a task is being executed, it won't have a provider message yet
     if current_provider_message and current_provider_message.status != BroadcastProviderMessageStatus.SENDING: