Able to Unsubscribe from Repositories without being Subscribed #546

Normally, users with control of the plugin might want to unsubscribe from repos/users/orgs that they're subscribed to, and this works fine. However, I noticed that you can "unsubscribe" from literally anything at all. It doesn't matter what you put after the unsubscribe keyword or the unsubscribe delete command. This command should obviously be filtered to only show a "successfully unsubscribed" message when unsubscribing from a subscribed repo/user/org.

I would be happy to work on a fix for this if someone can assign me this issue. Thanks for reading!