[FIX] sale: traceback when choosing a product with warning as order.line

If a user chooses a product that has a blocking error message, the product
is set to False. This is good, but we do not want the following to happen:

The other onchange triggers are called and "product_uom_change"
generates an error because there is no product. (In fact it is
"_compute_price_rule" on "product.pricelist" who raise)
The onchange update the values of the other fields related to the
product (eg for the "name" field where the name of the product that
is canceled by the warning is assigned).

addons/sale/models/sale.py

@@ -878,6 +878,21 @@ class SaleOrderLine(models.Model):
             uom=self.product_uom.id
         )
 
+        result = {'domain': domain}
+
+        title = False
+        message = False
+        warning = {}
+        if product.sale_line_warn != 'no-message':
+            title = _("Warning for %s") % product.name
+            message = product.sale_line_warn_msg
+            warning['title'] = title
+            warning['message'] = message
+            result = {'warning': warning}
+            if product.sale_line_warn == 'block':
+                self.product_id = False
+                return result
+
         name = product.name_get()[0][1]
         if product.description_sale:
             name += '\n' + product.description_sale
@@ -889,22 +904,11 @@ class SaleOrderLine(models.Model):
             vals['price_unit'] = self.env['account.tax']._fix_tax_included_price(self._get_display_price(product), product.taxes_id, self.tax_id)
         self.update(vals)
 
-        title = False
-        message = False
-        warning = {}
-        if product.sale_line_warn != 'no-message':
-            title = _("Warning for %s") % product.name
-            message = product.sale_line_warn_msg
-            warning['title'] = title
-            warning['message'] = message
-            if product.sale_line_warn == 'block':
-                self.product_id = False
-            return {'warning': warning}
-        return {'domain': domain}
+        return result
 
     @api.onchange('product_uom', 'product_uom_qty')
     def product_uom_change(self):
-        if not self.product_uom:
+        if not self.product_uom or not self.product_id:
             self.price_unit = 0.0
             return
         if self.order_id.pricelist_id and self.order_id.partner_id: