Description:
------------
imagescale adds a bottom and right black border if the mode used is IMG_BICUBIC

This is dependant on the GD version not PHP version

GD versions that fail:
The official Windows php.exe (7.4.5) uses GD "bundled (2.1.0 compatible)"
The official Windows php.exe (7.2.30) uses GD "bundled (2.1.0 compatible)"
http://phpfiddle.org/ (PHP 7.1.18) uses GD "bundled (2.1.0 compatible)"
One of my site hosts (PHP 7.0.33) uses GD "bundled (2.1.0 compatible)"

GD versions that pass:
https://rextester.com/ (PHP 7.2.24) uses GD 2.2.5
https://paiza.io/ (PHP 7.4.1) uses GD 2.2.5
https://www.tutorialspoint.com/ (PHP 7.1.8) uses GD 2.2.4

LibGD 2.3.0 (March 2020) contains security fixes
PHP 7.4.5 source file "ext/gd/libgd/gd.h" defines GD version as 2.0.35 (<=2015)










Test script:
---------------
function test($image, $desc) {
echo $desc . ' - Test Result: ' . (imagecolorat($image, imagesx($image) - 1 , imagesy($image) - 1) != 0x000000 ? 'pass' : 'fail') . '<br>';
//line below displays image
//ob_start(); imagepng($image); $imageString = ob_get_clean();echo '<img src="data:image/png;base64, ' . base64_encode($imageString) . '" /><br><br>';
}
echo 'PHP: ' . phpversion(). ' GD: ' . gd_info()["GD Version"] . '<br>';
$size = 32;
$src = imagecreatetruecolor($size, $size);
imagefilledrectangle($src, 0, 0, $size - 1 , $size - 1, 0xff00ff);//magenta
test($src, 'No scaling');
test(imagescale($src, $size * 2, $size * 2), 'Scale 200%, default mode');
test(imagescale($src, $size / 2, $size / 2), 'Scale 50%, default mode');
test(imagescale($src, $size * 2, $size * 2, IMG_BICUBIC), 'Scale 200%, IMG_BICUBIC mode');
test(imagescale($src, $size / 2, $size / 2, IMG_BICUBIC), 'Scale 50%, IMG_BICUBIC mode');