Load: Only load PasswordHash class when needed.

This reverts [38371] which loaded `class-phpass.php` early in `wp-settings.php` and in turn caused backward compatibility problems.

Props DavidAnderson, ketuchetan.
Fixes #39445.


git-svn-id: https://develop.svn.wordpress.org/trunk@40387 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/post-template.php

@@ -793,6 +793,7 @@ function post_password_required( $post = null ) {
 		return apply_filters( 'post_password_required', true, $post );
 	}
 
+	require_once ABSPATH . WPINC . '/class-phpass.php';
 	$hasher = new PasswordHash( 8, true );
 
 	$hash = wp_unslash( $_COOKIE[ 'wp-postpass_' . COOKIEHASH ] );