[FIX] website_sale_loyalty: Stop getting succes message after applying invalid coupon

Current Behaviour:
In E-commerce, when you apply a ``LoyaltyCard`` which is not applicable on the ``SaleOrder``,
in a specific case it displays a success message even if the coupon is not applied.

Expected behaviour
Don't display a success message when the coupon is not applicable

Steps:
- Create a program with 'coupon' type, a rule of 'minimum 1' and a reward on a specific product A.
- Generate a coupon
- Go to shop add product A to the cart, go to checkout and apply the coupon code(Everything goes well).
- Delete the coupon and the product, and add a product B.
- Go to checkout and try to apply the same coupon code.

Issue:
Wrong success message

Reason:
The wrong message is displayed beacause on the python side we just check if there
is 'error' in the ``Request.session`` but in this case there is also 'error_promo_code'
that should be considered.

opw-3355632

closes odoo/odoo#129663

X-original-commit: 6ee60a30e0798ce69152385b08e49b223782d785
Signed-off-by: Victor Feyens (vfe) <vfe@odoo.com>
Signed-off-by: Eteil Junior Djoumatchoua (etdj) <etdj@odoo.com>

addons/website_sale_loyalty/controllers/main.py

@@ -15,17 +15,19 @@ class WebsiteSale(main.WebsiteSale):
     def pricelist(self, promo, **post):
         order = request.website.sale_get_order()
         coupon_status = order._try_apply_code(promo)
-        if 'error' not in coupon_status:
-            if len(coupon_status) == 1:
-                coupon, rewards = next(iter(coupon_status.items()))
-                if len(rewards) == 1 and not rewards.multi_product:
-                    self._apply_reward(order, rewards, coupon)
         if coupon_status.get('not_found'):
             return super(WebsiteSale, self).pricelist(promo, **post)
         elif coupon_status.get('error'):
             request.session['error_promo_code'] = coupon_status['error']
-        if 'error' not in coupon_status:
-            request.session['successful_code'] = promo
+        elif 'error' not in coupon_status:
+            reward_successfully_applied = True
+            if len(coupon_status) == 1:
+                coupon, rewards = next(iter(coupon_status.items()))
+                if len(rewards) == 1 and not rewards.multi_product:
+                    reward_successfully_applied = self._apply_reward(order, rewards, coupon)
+
+            if reward_successfully_applied:
+                request.session['successful_code'] = promo
         return request.redirect(post.get('r', '/shop/cart'))
 
     @http.route()
@@ -102,10 +104,20 @@ class WebsiteSale(main.WebsiteSale):
         return request.redirect(redirect)
 
     def _apply_reward(self, order, reward, coupon):
+        """Try to apply the given program reward
+
+        :returns: whether the reward was successfully applied
+        :rtype: bool
+        """
         try:
-            order._apply_program_reward(reward, coupon)
+            reward_status = order._apply_program_reward(reward, coupon)
         except UserError as e:
             request.session['error_promo_code'] = str(e)
+            return False
+        if 'error' in reward_status:
+            request.session['error_promo_code'] = reward_status['error']
+            return False
+        return True
 
     @http.route()
     def cart_update_json(self, *args, set_qty=None, **kwargs):