Feature request: prevent self messaging in existing conversations with self

[rygine]

Is your feature request related to a problem?

with this PR, the ability to start a conversation with yourself was removed. however, if you already had a conversation started with yourself, you're still able to send messages to it.

Describe the solution to the problem

the solution is to also block sending messages to yourself in a pre-existing conversation with yourself

Describe the uses cases for the feature

this just closes the loop on the regression of being able to start a conversation with yourself

Additional details

No response