Fix PHP 8.1 "strlen(null)" exception creating a Portal

Summary:
`strlen()` was used in Phabricator to check if a generic value is a non-empty string.
This behavior is deprecated since PHP 8.1. Phorge adopts `phutil_nonempty_string()` as a replacement.

Note: this may highlight other absurd input values that might be worth correcting
instead of just ignoring. If phutil_nonempty_string() throws an exception in your
instance, report it to Phorge to evaluate and fix that specific corner case.

```
ERROR 8192: strlen(): Passing null to parameter #1 ($string) of type string is deprecated at [/var/www/html/phorge/phorge/src/applications/dashboard/menuitem/PhabricatorDashboardPortalMenuItem.php:34]
```

Closes T15847

Test Plan: Go to `/portal/edit/form/default/`, set a name and click `Create Portal`.

Reviewers: O1 Blessed Committers, valerio.bozzolan

Reviewed By: O1 Blessed Committers, valerio.bozzolan

Subscribers: tobiaswiese, valerio.bozzolan, Matthew, Cigaryno

Maniphest Tasks: T15847

Differential Revision: https://we.phorge.it/D25681

src/applications/dashboard/menuitem/PhabricatorDashboardPortalMenuItem.php

@@ -31,7 +31,7 @@ final class PhabricatorDashboardPortalMenuItem
     PhabricatorProfileMenuItemConfiguration $config) {
     $name = $config->getMenuItemProperty('name');
 
-    if (strlen($name)) {
+    if (phutil_nonempty_string($name)) {
       return $name;
     }