[FIX] sale: Uom field readonly for new sale order lines

closes odoo/odoo#122683

X-original-commit: 2e5c8b4eb427e580ed22417ff49cf3cb994ba88d
Signed-off-by: Victor Feyens (vfe) <vfe@odoo.com>

addons/sale/models/sale_order_line.py

@@ -889,7 +889,8 @@ class SaleOrderLine(models.Model):
     @api.depends('state')
     def _compute_product_uom_readonly(self):
         for line in self:
-            line.product_uom_readonly = line.state in ['sale', 'done', 'cancel']
+            # line.ids checks whether it's a new record not yet saved
+            line.product_uom_readonly = line.ids and line.state in ['sale', 'done', 'cancel']
 
     #=== CONSTRAINT METHODS ===#