Add sanity checks in map_meta_cap(), return 'do_not_allow' when posts don't exist.

Adds unit test.

Props ocean90, nerrad, filosofo.
Fixes #23162.


git-svn-id: https://develop.svn.wordpress.org/trunk@34113 602fd350-edb4-49c9-b593-d223f7449a82

tests/phpunit/tests/user/mapMetaCap.php

@@ -37,6 +37,16 @@ class Tests_User_MapMetaCap extends WP_UnitTestCase {
 		parent::tearDown();
 	}
 
+	/**
+	 * @ticket 13905
+	 */
+	function test_capability_type_post_with_invalid_id() {
+		$this->assertEquals(
+			array( 'do_not_allow' ),
+			map_meta_cap( 'edit_post', $this->user_id, $this->post_id + 1 )
+		);
+	}
+
 	function test_capability_type_post_with_no_extra_caps() {
 
 		register_post_type( $this->post_type, array(