Bug: Newline in message content deletes message for quoting

[jkriste]

Message quoting deletes the message if the message being linked is by itself on a newline.

For example, the following message content will be deleted:

testing testing 123
https://discord.com/channels/386585461285715968/386585461285715971/1150578939488645191

but the following message will not be deleted:

testing testing 123
https://discord.com/channels/386585461285715968/386585461285715971/1150578939488645191 test

Solution: modify the regex in handle_message_links in message_handling_service.py