now starts the session if it's not already running

Public/FormHandling/Login.php

@@ -38,6 +38,10 @@ if (!password_verify($sha512Hash, $result['PasswordHash']))
     die();
 }
 
+if (session_status() == PHP_SESSION_NONE) {
+    session_start();
+}
+
 $_SESSION[SessionElement::IS_LOGGED_IN->value] = true;
 $_SESSION[SessionElement::USER_ID->value] = $result['ID'];
 $_SESSION[SessionElement::USERNAME->value] = $result['Username'];