Update callback.php

update from https://github.com/edgardmessias/glpi-singlesignon/pull/87

front/callback.php

@@ -92,8 +92,8 @@ if ($user_id || $signon_provider->login()) {
 
    if (isset($params['redirect'])) {
       $REDIRECT = '?redirect=' . $params['redirect'];
-   } else if (isset($_GET['state']) && is_integer(strpos($_GET['state'], "&redirect="))) {
-      $REDIRECT = '?' . substr($_GET['state'], strpos($_GET['state'], "&redirect=") + 1);
+   } else if (isset($_GET['state']) && is_integer(strpos($_GET['state'], ";redirect="))) {
+      $REDIRECT = '?' . substr($_GET['state'], strpos($_GET['state'], ";redirect=") + 1);
    }
 
    if ($_SESSION["glpiactiveprofile"]["interface"] == "helpdesk") {