Description:
------------
When using ob_start with a custom calback ob_gzhandler tries resending headers and also generate a corrupted output.

Both generates same headers with exception of:
//Response Headers
Keep-Alive: timeout=5, max=100 // Script with fine Output
Keep-Alive: timeout=5, max=99 // Script with bad output

//Request Headers
Sec-Fetch-Site: none        // Script with fine Output
Sec-Fetch-Site: same-origin // Script with bad Output

Test script:
---------------
// Script with fine Output
<?php
header( 'Content-type: text/html; charset=utf-8' );
ob_start("ob_gzhandler");
echo 'Begin ...<br />';
for( $i = 0 ; $i < 5 ; $i++ )
{
    echo $i . '<br />';
    ob_end_flush();
    flush();
    ob_flush();
    ob_start("ob_gzhandler");
    sleep(1);
}
echo 'End ...<br />';





// Script with bad Output
<?php
function ob_chunked_gzhandler($buffer, $phase)
{ //compression on
    $buffer                = ob_gzhandler($buffer, $phase);//<--fourth line
    $length                 = strlen($buffer);
    return dechex($length) . "\r\n$buffer\r\n";
}

header('Content-type: text/html; charset=utf-8');
ob_start("ob_chunked_gzhandler");
echo 'Begin ...<br />';
for ($i = 0; $i < 10; $i++) {
    echo $i . '<br />';
    ob_end_flush();
    flush();
    ob_flush();
    ob_start("ob_chunked_gzhandler");
    sleep(1);
}
echo 'End ...<br />';


Expected result:
----------------
//Outputs fine:
Begin ...
0
1
2
3
4
End ...

Actual result:
--------------
55RW sJM��S��ӳI*Rз3�P���2 1b � 3�I*RзR�4) 1b � 3�I*Rзσ� 1b � 3�I*Rз{��� 1b � 3�I*Rз��{ 1b � 3�I*RзA�{� 1b � 3�I*Rзܧ�� 1b � 3�I*Rзh��J 1b � ��I*Rз�ܬ� 1b � ��I*Rз5�� 21 � s�KQ��ӳI*Rз��B


//Error.log file
[Thu Aug 27 11:53:48.261150 2020] [fcgid:warn] [pid 17632:tid 1148] [client ::1:6687] mod_fcgid: stderr: PHP Warning:  Cannot modify header information - headers already sent by (output started at C:\\server\\lec\\var\\www\\output_custom.php:16) in C:\\server\\lec\\var\\www\\output_custom.php on line 4, referer: http://localhost/