Description:
------------
When reading images with imagecreatefromwebp() all colors are
shifted.

This issue has already been reported upstream against libgd:
<https://github.com/libgd/libgd/issues/83>.

Test script:
---------------
<?php
$im = imagecreatetruecolor(8, 8);
$white = imagecolorallocate($im, 0xff, 0xaa, 0x55);
echo sprintf("%08x\n", $white);
imagefilledrectangle($im, 0, 0, 74, 74, $white);
imagewebp($im, 'test.webp');
imagedestroy($im);

$im = imagecreatefromwebp('test.webp');
echo sprintf("%08x\n", imagecolorat($im, 4, 4));
imagepng($im, 'test.png');
?>


Expected result:
----------------
00ffaa55
00ffaa55

Actual result:
--------------
00ffaa55
ffab5500