[FIX] mail: set the parent_id to the first message of type email

And fallback of any type if there is none of type email

This fix allow the communication between two mail thread from two different Odoo servers having message creation subtypes, like project issue or crm lead

addons/mail/mail_thread.py

@@ -1166,7 +1166,9 @@ def message_post(self, cr, uid, thread_id, body='', subject=None, type='notifica
 
         # _mail_flat_thread: automatically set free messages to the first posted message
         if self._mail_flat_thread and not parent_id and thread_id:
-            message_ids = mail_message.search(cr, uid, ['&', ('res_id', '=', thread_id), ('model', '=', model)], context=context, order="id ASC", limit=1)
+            message_ids = mail_message.search(cr, uid, ['&', ('res_id', '=', thread_id), ('model', '=', model), ('type', '=', 'email')], context=context, order="id ASC", limit=1)
+            if not message_ids:
+                message_ids = message_ids = mail_message.search(cr, uid, ['&', ('res_id', '=', thread_id), ('model', '=', model)], context=context, order="id ASC", limit=1)
             parent_id = message_ids and message_ids[0] or False
         # we want to set a parent: force to set the parent_id to the oldest ancestor, to avoid having more than 1 level of thread
         elif parent_id: