[FIX] sale_loyalty: round real points for coupon

`_get_real_points_for_coupon` subtracts several floats which can result
in rounding errors when a comparison is made in `action_confirm` that
checks if the result is smaller than 0. If the result is something like
-1 * 10^-14, Odoo will tell the user the coupon is invalid, which is
false. To prevent this from happening, we round according to the
associated currency of the points.

opw-3120442

closes odoo/odoo#112995

X-original-commit: 59c43f5cc460f311388540558e0fb0731b02cbc2
Signed-off-by: Yannick Tivisse (yti) <yti@odoo.com>

addons/sale_loyalty/models/sale_order.py

@@ -494,6 +494,7 @@ class SaleOrder(models.Model):
             points += self.coupon_point_ids.filtered(lambda p: p.coupon_id == coupon).points
         # Points already used by rewards
         points -= sum(self.order_line.filtered(lambda l: l.coupon_id == coupon).mapped('points_cost'))
+        points = coupon.currency_id.round(points)
         return points
 
     def _add_points_for_coupon(self, coupon_points):