Improve check for product categories (#59)

Summary:
This update checks whether the product is within a category.

There are sites where it is possible that the product is not even in the `Uncategorized` "fallback" category.

Pull Request resolved: #59

Reviewed By: maxkozin

Differential Revision: D66595736

Pulled By: vahidkay-meta

fbshipit-source-id: aa62905081553726cba962bbdfbd494d7496ab1d

integration/FacebookWordpressWooCommerce.php

@@ -123,7 +123,8 @@ private static function getProductCategory($product_id){
         $product_id,
         'product_cat'
       );
-    return count($categories) > 0 ? $categories[0]->name : null;
+
+    return (is_array($categories) && count($categories) > 0) ? $categories[0]->name : null;
   }
 
   public static function trackPurchaseEvent($order_id) {