Description:
------------
Recursion detected on calling mb_convert_variables with nested array

Test script:
---------------
<?php

$test = array (
    0 => array (
    )
);

mb_convert_variables('utf-8', 'cp1251', $test);

var_dump($test);

mb_convert_variables('utf-8', 'utf-8', $test);

var_dump($test);


// here another example

for ($i = 0; $i < 2; ++$i) {
    $test = array (
        0 => array()
    );

    $data = json_decode(json_encode($test), 1);

    mb_convert_variables('utf-8', 'cp1251', $data);

    var_dump($data);
}


Expected result:
----------------
no error