iss1217 - Fix mathjax url for PHP 8.2

vle_specific.php

@@ -204,7 +204,7 @@ function stack_get_mathjax_url(): string {
             $urlstring = substr($mathjaxconfigurl, 0, $questionpos);
             parse_str($querystring, $queryparams);
             $queryparams = array_merge(['config' => 'TeX-AMS-MML_HTMLorMML'], $queryparams);
-            $querystring = http_build_query($queryparams, null, '&', PHP_QUERY_RFC3986);
+            $querystring = http_build_query($queryparams, '', '&', PHP_QUERY_RFC3986);
             $url = $urlstring . '?' . $querystring;
         } else {
             $url = $mathjaxconfigurl . '?config=TeX-AMS-MML_HTMLorMML';