lingo: include query string in amount computation (#9174)

combo/apps/lingo/views.py

@@ -69,6 +69,7 @@ class AddBasketItemApiView(View):
         extra = request_body.get('extra', {})
 
         item = BasketItem(amount=0)
+        item.amount = sum([Decimal(x) for x in request.GET.getlist('amount')])
 
         if request_body.get('amount'):
             item.amount += self.get_amount(request_body['amount'])