chore: ensure post_id is not lost when constructing Box with invalid post ID

Author: dannyvankooten

src/class-box.php

@@ -43,10 +43,11 @@ public function __construct($post)
     {
         // fetch post if it hasn't been fetched yet
         if (! $post instanceof WP_Post) {
-            $post = get_post($post);
+            $post_id = $post;
+            $post = get_post($post_id);
 
             if ($post === null) {
-                throw new \InvalidArgumentException('No post found with ID ' . $post);
+                throw new \InvalidArgumentException('No post found with ID ' . $post_id);
             }
         }