The sender PID of the notification was being set to the target PID,
instead of the sender PID. Use correct PID and remove redundant target
PID argument.
Also fix minor accuracy issues.
Now that we can return errors to nex-protocols-go and it will handle it,
we can improve how errors are being handled in friends.
There's probably room for improvement from this, since I haven't added
error handling on some database getters due to uncertainties on whether
the error should interrupt an action or not.