Fix more PHP 8.1 "strlen(null)" callsites in PhutilURI

Summary: Ref T13676. Ref T13588. These properties on PhutilURI have flexible types, just wrap them.

Test Plan: Built a new Drydock working copy with an HTTPS URI under PHP 8.1, see T13676.

Maniphest Tasks: T13676, T13588

Differential Revision: https://secure.phabricator.com/D21798