Description:
------------
Repeately calling iptcembed() causes a superfluous FF byte to be
added with each call. While this may not be a violation of the
JFIF standard (the specs are not publicly available, apparently),
I'd nonetheless consider this a bug, because repeated embedding of
the same metadata should not result in different files.


Test script:
---------------
<?php
$filename = __DIR__ . '/test.jpg';
@unlink($filename);
$im = imagecreatetruecolor(10, 10);
imagejpeg($im, $filename);
imagedestroy($im);
$data = "\x1C\x02x\x00\x0ATest image"
    . "\x1C\x02t\x00\x22Copyright 2008-2009, The PHP Group";
$content = iptcembed($data, $filename);
$fp = fopen($filename, "wb");
fwrite($fp, $content);
fclose($fp);
echo filesize($filename), PHP_EOL;
clearstatcache();
$content = iptcembed($data, $filename);
$fp = fopen($filename, "wb");
fwrite($fp, $content);
fclose($fp);
echo filesize($filename), PHP_EOL;
?>


Expected result:
----------------
779
779


Actual result:
--------------
779
780