MAGETWO-98522: Adding out of stock items to comparison shows success message but fails

- Fix CR comments

Author: YuliyaLabudova

app/code/Magento/Catalog/ViewModel/Product/Checker/AddToCompareAvailability.php

@@ -37,8 +37,7 @@ public function __construct(StockConfigurationInterface $stockConfiguration)
      */
     public function isAvailableForCompare(ProductInterface $product): bool
     {
-        return $this->isInStock($product) ||
-            !$this->isInStock($product) && $this->stockConfiguration->isShowOutOfStock();
+        return $this->isInStock($product) || $this->stockConfiguration->isShowOutOfStock();
     }
 
     /**
@@ -54,8 +53,6 @@ private function isInStock(ProductInterface $product): bool
             return $product->isSalable();
         }
 
-        return isset($quantityAndStockStatus['is_in_stock'])
-            ? $quantityAndStockStatus['is_in_stock']
-            : false;
+        return isset($quantityAndStockStatus['is_in_stock']) && $quantityAndStockStatus['is_in_stock'];
     }
 }