Fix path checking for the existence of a namespaced helper file

Author: yllumi

system/Common.php

@@ -598,7 +598,7 @@ function helper($filenames): void
             if (str_contains($filename, '\\')) {
                 $path = $loader->locateFile($filename, 'Helpers');
 
-                if ($path !== '') {
+                if (!$path) {
                     throw FileNotFoundException::forFileNotFound($filename);
                 }