[FIX] crm: make sure there is a create date when computing date_open

Display the field date_open in the crm.lead form view
Create a new record

Before this commit, there was a crash because since the record is a virtual one
there is no create_date, hence the crash

After this commit, we make sure we select records that have a create_date, and there is no crash

OPW 1877080
closes #26499

addons/crm/models/crm_lead.py

@@ -166,7 +166,7 @@ class Lead(models.Model):
     @api.depends('date_open')
     def _compute_day_open(self):
         """ Compute difference between create date and open date """
-        for lead in self.filtered(lambda l: l.date_open):
+        for lead in self.filtered(lambda l: l.date_open and l.create_date):
             date_create = fields.Datetime.from_string(lead.create_date)
             date_open = fields.Datetime.from_string(lead.date_open)
             lead.day_open = abs((date_open - date_create).days)
@@ -174,7 +174,7 @@ class Lead(models.Model):
     @api.depends('date_closed')
     def _compute_day_close(self):
         """ Compute difference between current date and log date """
-        for lead in self.filtered(lambda l: l.date_closed):
+        for lead in self.filtered(lambda l: l.date_closed and l.create_date):
             date_create = fields.Datetime.from_string(lead.create_date)
             date_close = fields.Datetime.from_string(lead.date_closed)
             lead.day_close = abs((date_close - date_create).days)