Always call get_post() in get_page_uri() to ensure we have a WP_Post object,...

Always call get_post() in get_page_uri() to ensure we have a WP_Post object, which lazy-loads the ancestors this function requires.

props dd32
fixes #22883
Unit tests: [1175/tests]



git-svn-id: https://core.svn.wordpress.org/trunk@23208 1a063a9b-81f0-0310-95a4-ce76da25c4cd