Handle when a reply's referenced message is deleted

[engineereng]

A reply's referenced message is the message that the reply is replying to. It is possible for the referenced message to be deleted after the reply is made, which causes Discord to display the text "Original message deleted" in italics:

The log currently does not handle this case.

To Reproduce
Steps to reproduce the behavior:

1. Create a thread
2. Send a message ("Message A")
3. Create a reply to Message A
4. Delete Message A.
5. Use /archive this to log the thread.

Expected behavior
The log should have a reply-like system message that mimics the Discord: