Update InputFilter.php (#43377)

Author: AlterBrains

libraries/src/Filter/InputFilter.php

@@ -454,7 +454,7 @@ function ($m) {
         $source = preg_replace_callback(
             '/&#x([a-f0-9]+);/mi',
             function ($m) {
-                return mb_convert_encoding(\chr('0x' . $m[1]), 'UTF-8', 'ISO-8859-1');
+                return mb_convert_encoding(\chr(\hexdec($m[1])), 'UTF-8', 'ISO-8859-1');
             },
             $source
         );