[FIX] base_action_rule: Add followers in automated actions

When registering a payment on an account invoice with an automated
action which adds a follower "On Creation & Update", the function
recompute was triggered(due to the field residual_company_signed)
and the same followers was added two times for the invoice.

The fix avoid to unlink and create the same followers several
times(because it was the case with the function "_add_follower_command")

opw:690939

addons/base_action_rule/base_action_rule.py

@@ -194,7 +194,11 @@ class base_action_rule(osv.osv):
 
         # subscribe followers
         if self.act_followers and hasattr(records, 'message_subscribe'):
-            records.message_subscribe(self.act_followers.ids)
+            followers = self.env['mail.followers'].sudo().search([
+            ('res_model', '=', records._name), ('res_id', 'in', records.ids),
+            ('partner_id', 'in', self.act_followers.ids)])
+            if not len(followers) == len(self.act_followers):
+                records.message_subscribe(self.act_followers.ids)
 
         # execute server actions
         if self.server_action_ids: