Eliminate PHP notices. Thanks to Pablo Alvarez de Sotomayor Posadillo

functions/auth.php

@@ -199,7 +199,7 @@ function digest_md5_response ($username,$password,$challenge,$service,$host,$aut
  */
 function digest_md5_parse_challenge($challenge) {
     $challenge=base64_decode($challenge);
-    while (isset($challenge)) {
+    while (isset($challenge) && $challenge !== FALSE) {
         if ($challenge{0} == ',') { // First char is a comma, must not be 1st time through loop
             $challenge=substr($challenge,1);
         }