Description:
------------
ob_start() can nest as the description in php manual:
"Output buffers are stackable, that is, you may call ob_start() while another ob_start() is active."
But ob_start("ob_iconv_handler")  CAN'T.

Reproduce code:
---------------
<?php
/**
* Test: Can I nest ob_start("ob_iconv_handler") ?
*
* Result&#65306;I can't. It stop at internal nesting when meet a Chinese word.
*/
iconv_set_encoding("internal_encoding", "GB2312");
iconv_set_encoding("output_encoding", "UTF-8");

ob_start("ob_iconv_handler");

?>
<p>
    ALTER DATABASE&#29992;&#20110;&#26356;&#25913;&#25968;&#25454;&#24211;&#30340;&#20840;&#23616;&#29305;&#24615;&#12290;
</p>
<?
ob_start("ob_iconv_handler");
?>
<p>
    ALTER DATABASE&#29992;&#20110;&#26356;&#25913;&#25968;&#25454;&#24211;&#30340;&#20840;&#23616;&#29305;&#24615;&#12290;
</p>
<?
ob_end_flush();
ob_end_flush();
?>



Expected result:
----------------
 ALTER DATABASE&#29992;&#20110;&#26356;&#25913;&#25968;&#25454;&#24211;&#30340;&#20840;&#23616;&#29305;&#24615;&#12290;

ALTER DATABASE&#29992;&#20110;&#26356;&#25913;&#25968;&#25454;&#24211;&#30340;&#20840;&#23616;&#29305;&#24615;&#12290; 

Actual result:
--------------
 ALTER DATABASE&#29992;&#20110;&#26356;&#25913;&#25968;&#25454;&#24211;&#30340;&#20840;&#23616;&#29305;&#24615;&#12290;

ALTER DATABASE