Users: Clarify the return value of `get_current_user_id()` for non-logged-in users.

Props ovenall
Fixes #39051

Built from https://develop.svn.wordpress.org/trunk@39486


git-svn-id: http://core.svn.wordpress.org/trunk@39426 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/user.php

@@ -420,7 +420,7 @@ function count_many_users_posts( $users, $post_type = 'post', $public_only = fal
  *
  * @since MU
  *
- * @return int The current user's ID
+ * @return int The current user's ID, or 0 if no user is logged in.
  */
 function get_current_user_id() {
 	if ( ! function_exists( 'wp_get_current_user' ) )

wp-includes/version.php

@@ -4,7 +4,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '4.8-alpha-39483';
+$wp_version = '4.8-alpha-39486';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.