Fix PHP 8.1 "strlen(null)" exception which blocks rendering the "Manage Menu" page
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.
However, the parameter `$item_id` is a numeric value when populated.
Thus replace `strlen()` with `phutil_nonempty_scalar()` as `phutil_nonempty_string()` could break a Conduit API consumer sending a numeric value.
Note: this may highlight other absurd input values that might be worth correcting
instead of just ignoring. If phutil_nonempty_scalar() throws an exception in your
instance, report it to Phorge to evaluate and fix that specific corner case.
Closes T15317
Test Plan: Applied this change and `/home/menu/configure/` rendered in web browser.
Reviewers: O1 Blessed Committers, valerio.bozzolan
Reviewed By: O1 Blessed Committers, valerio.bozzolan
Subscribers: speck, tobiaswiese, valerio.bozzolan, Matthew, Cigaryno
Maniphest Tasks: T15317
Differential Revision: https://we.phorge.it/D25166