[Web] Some minor fixes and improvements for PHP 8

data/web/inc/header.inc.php

@@ -110,7 +110,7 @@
             <?php foreach ($MAILCOW_APPS as $app) {
               if (getenv('SKIP_SOGO') == "y" && preg_match('/^\/SOGo/i', $app['link'])) { continue; }
             ?>
-              <li title="<?= htmlspecialchars($app['description']); ?>"><a href="<?= htmlspecialchars($app['link']); ?>"><?= htmlspecialchars($app['name']); ?></a></li>
+              <li title="<?=(isset($app['description'])) ? htmlspecialchars($app['description']) : '';?>"><a href="<?=(isset($app['link'])) ? htmlspecialchars($app['link']) : '';?>"><?=(isset($app['name'])) ? htmlspecialchars($app['name']) : '';?></a></li>
             <?php
             }
             $app_links = customize('get', 'app_links');