Description:
------------
when call restore_error_handler() inside an error handler function, it not works.

Reproduce code:
---------------
<?php

function t35_handler($no, $msg){
    echo __LINE__.__METHOD__."\n";
    restore_error_handler();
    echo __LINE__.__METHOD__."\n";
}
function t35(){
    echo "old handler=".set_error_handler("t35_handler")."\n";
    trigger_error("error1");
    echo "old handler=".set_error_handler("t35_handler")."\n";
    trigger_error("error2");
}


?>

Expected result:
----------------
old handler=
4t35_handler
6t35_handler
old handler=
4t35_handler
6t35_handler


Actual result:
--------------
old handler=
4t35_handler
6t35_handler
old handler=t35_handler
4t35_handler
6t35_handler