R1:562d36ef5f9e

Fix PHP 8.1 "strlen(null)" exceptions to render the Account Creation page

Summary:
Fix numerous PHP 8.1 "strlen(null)" exceptions which block rendering the initial Account
Creation page in a fresh Phorge installation.

The strlen() was used in Phabricator to check if a generic value was a non-empty string.
For this reason, Phorge adopts phutil_nonempty_string() that checks that.

Note: this may highlight other absurd input values that might be worth correcting
instead of just ignoring. If your…