ACP2E-285: Add to cart failed when cart total is zero and cart price rule is Fixed amount discount for whole cart

Author: Chhandak.Barua

app/code/Magento/SalesRule/Helper/CartFixedDiscount.php

@@ -127,7 +127,7 @@ public function getShippingDiscountAmount(
         float $shippingAmount,
         float $quoteBaseSubtotal
     ): float {
-        $ratio = $shippingAmount / $quoteBaseSubtotal;
+        $ratio = $quoteBaseSubtotal != 0 ? $shippingAmount / $quoteBaseSubtotal : 0;
         return $this->priceCurrency
             ->roundPrice(
                 $rule->getDiscountAmount() * $ratio