fix(talkbot): reply to image messages with translated captions

containers/talkbot/server.py

@@ -1241,6 +1241,11 @@ def process_event(job: dict) -> None:
     preserve_original = job.get("preserve_original", False)
     reply_to_message_id = job.get("reply_to_message_id")
 
+    # A caption attached to an image is not itself an inReplyTo event. In
+    # that case the translation must reply to the image message itself.
+    if preserve_original and reply_to_message_id is None:
+        reply_to_message_id = message_id
+
     try:
         recipients = get_target_user_ids(
             token,