system/request: guard session_start() with session_status()

[krzsztf1]

Session::__construct() in webui/system/request.php calls session_start()
unconditionally:

class Session {
   public function __construct() {
      session_start();
   }

When the class is instantiated while a session is already active, PHP logs:

PHP Notice: session_start(): Ignoring session_start() because a session is
already active (started from /var/piler/www/system/request.php on line 30)
in /var/piler/www/system/request.php on line 30

The file effectively warns about itself, which is confusing when tracking down
session problems.

This happens in piler's own SSO entry point. webui/sso.php starts a session
three times in a single request:

session_start();                 // line 2
require_once("config.php");      // line 6 -> config.php:405 does new Session()
$session = new Session();        // line 10

Guarding with session_status() makes the constructor idempotent. On a fresh
request nothing changes: session_status() returns PHP_SESSION_NONE and
session_start() runs exactly as before.

Environment: piler 1.4.9, PHP 8.5, Ubuntu 26.04.

[jsuto]

Thank you!