[FIX] sale: Traceback when changing date order

When the user removes the readonly from the field date order and tries
to modify it it crashes in some cases, this commit fix this

opw-2523508

closes odoo/odoo#70969

X-original-commit: 3e4a541277828ec9cd0bd97587c6d87dc91ccf08
Signed-off-by: Achraf <abz-odoo@users.noreply.github.com>

addons/sale/models/sale.py

@@ -1099,7 +1099,7 @@ class SaleOrderLine(models.Model):
 
     def _expected_date(self):
         self.ensure_one()
-        order_date = fields.Datetime.from_string(self.order_id.date_order if self.order_id.state in ['sale', 'done'] else fields.Datetime.now())
+        order_date = fields.Datetime.from_string(self.order_id.date_order if self.order_id.date_order and self.order_id.state in ['sale', 'done'] else fields.Datetime.now())
         return order_date + timedelta(days=self.customer_lead or 0.0)
 
     @api.depends('product_uom_qty', 'discount', 'price_unit', 'tax_id')