fix: guard

Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>

Author: WezSieTato

lib/validateEAN.js

@@ -28,4 +28,4 @@ function validateEAN(elem) {
     return num === parseInt(elem[elem.length - 1], 10);
 }
 
-if (typeof module !== 'undefined') module.exports = { validateEAN };
+if (typeof module !== 'undefined' && module.exports) module.exports = { validateEAN };