[FIX] crm: fix partner_id while converting a lead to an opportunity

Prerequisites

    - Configure a mail server (incoming)
    - Enable leads in CRM app
    - Create a sales team with a mail alias (ex: testcrm@odoo.com)
      and check "Pipeline" and "Leads"
    - Set a partner email with one of yours (ex: bob@odoo.com) /!\
    - Send a mail from bob to testcrm
    - In the incoming mail server click on "Fetch"

Reproduce the issue:

    - Convert the generated lead to an opportunity
    - Choose "Existing customer" and set another one than the actual
    - The opportunity is created but the customer is the old one

Cause:

    The given partner_id is overriden by the old one in the
    `handle_partner_assignation` method.

This commit gives the priority to the new partner_id.

OPW-2089404

closes odoo/odoo#40031

X-original-commit: e1833936255839cd34eba5758ca4c3124fd2522c
Signed-off-by: Jason Van Malder <jasonvanmalder@users.noreply.github.com>

addons/crm/models/crm_lead.py

@@ -950,6 +950,8 @@ class Lead(models.Model):
         """
         partner_ids = {}
         for lead in self:
+            if partner_id:
+                lead.partner_id = partner_id
             if lead.partner_id:
                 partner_ids[lead.id] = lead.partner_id.id
                 continue
@@ -957,8 +959,6 @@ class Lead(models.Model):
                 partner = lead._create_lead_partner()
                 partner_id = partner.id
                 partner.team_id = lead.team_id
-            if partner_id:
-                lead.partner_id = partner_id
             partner_ids[lead.id] = partner_id
         return partner_ids