Add @static* annotations where they are missing.

Initialize all static vars that are not, most to `null`.

See #32444.


git-svn-id: https://develop.svn.wordpress.org/trunk@32650 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/pomo/po.php

@@ -355,6 +355,7 @@ class PO extends Gettext_Translations {
 	/**
 	 * @staticvar string   $last_line
 	 * @staticvar boolean  $use_last_line
+	 * 
 	 * @param     resource $f
 	 * @param     string   $action
 	 * @return boolean