Description:
------------
Drawing very large antialised lines causes integer overflows in
gdImageAALine(), what can lead to strange results and even
crashes.

This issue had been reported upstream as
<https://github.com/libgd/libgd/issues/5> and fixed, but the fix
didn't yet make it to PHP's bundled libgd.


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

$im = imagecreatetruecolor(32768, 1);
$black = imagecolorallocate($im, 0, 0, 0);
imageantialias($im, true);

imageline($im, 0,0, 32767,0, $black);

imagepng($im, __DIR__ . DIRECTORY_SEPARATOR . 'aa-bug.png');


Expected result:
----------------
A PNG image with a line.

Actual result:
--------------
PHP crashes.