[IMP] im_livechat : avoid double notif for public livechat channel and clean method

As in super, we add uuid and message if channel is public
we have to exculde the public channel to add the same in a livechat case

Also, _channel_message_notifications is a bit rewritten to remove useless
code. Indeed, notifications will always be filled in as
_channel_message_notifications is only called by _notify that ensure that self
is not null and that message is singleton. In super, the notifications will then be
filled in and in override, no need to check if notifications is not empty.

We take the message dict from notif to avoid calling message_format a second time.

Task ID : 1895998
Closes PR #28283

addons/im_livechat/models/mail_channel.py

@@ -48,11 +48,10 @@ class MailChannel(models.Model):
             should be added to the notification, since the user cannot be listining to the channel.
         """
         notifications = super(MailChannel, self)._channel_message_notifications(message)
-        message_values_dict = notifications[0][1] if len(notifications) else dict(message.message_format()[0])
         for channel in self:
             # add uuid for private livechat channels to allow anonymous to listen
-            if channel.channel_type == 'livechat':
-                notifications.append([channel.uuid, message_values_dict])
+            if channel.channel_type == 'livechat' and channel.public == 'private':
+                notifications.append([channel.uuid, notifications[0][1]])
         if not message.author_id:
             unpinned_channel_partner = self.mapped('channel_last_seen_partner_ids').filtered(lambda cp: not cp.is_pinned)
             if unpinned_channel_partner: