Description:
------------
Forwarding from upstream[1] since PHP's bundled libgd is affected
as well.

Consider, for instance, an 8x8 pixel image with a white background
with a single black pixel anywhere (except for the corners).
Applying gdImageCropAuto(…, GD_CROP_SIDES) is supposed to yield a
1x1 pixel image with a black pixel. The test script is exercising
this for all 60 possible black pixel positions.

[1] <https://github.com/libgd/libgd/issues/485>

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

function createWhiteImageWithBlackPixelAt($x, $y)
{
    $im = imagecreatetruecolor(8, 8);
    imagefilledrectangle($im, 0, 0, 7, 7, 0xffffff);
    imagesetpixel($im, $x, $y, 0x000000);
    return $im;
}

$count = 0;
for ($y = 0; $y < 8; $y++) {
    for ($x = 0; $x < 8; $x++) {
        if (($x == 0 && ($y == 0 || $y == 7)) || ($x == 7 && ($y == 0 || $y == 7))) {
            continue; // skip the corners
        }
        $orig = createWhiteImageWithBlackPixelAt($x, $y);
        $cropped = imagecropauto($orig, IMG_CROP_SIDES);
        if ($cropped) {
            if (imagesx($cropped) === 1 && imagesy($cropped) === 1 && imagecolorat($cropped, 0, 0) === 0x000000) {
                $count++;
            }
            imagedestroy($cropped);
        }
        imagedestroy($orig);
    }
}

echo "$count\n";

Expected result:
----------------
60

Actual result:
--------------
0