Fix for Black -> White Background when converting from PNG->JPG

[ghost]

GdThumb.inc.php line 666:

    switch ($format) 
    {
        case 'GIF':
            imagegif($this->oldImage, $fileName);
            break;
        case 'JPG':
        if (file_exists($fileName))
        {
            $input =$this->oldImage;
            list($width, $height) = getimagesize($fileName);
                $output = imagecreatetruecolor($width, $height);
                $white = imagecolorallocate($output,  255, 255, 255);
                imagefilledrectangle($output, 0, 0, $width, $height, $white);
                imagecopy($output, $input, 0, 0, 0, 0, $width, $height);
                imagejpeg($output, $fileName);
        }
        else
        {
            imagejpeg($this->oldImage, $fileName, $this->options['jpegQuality']);
        }

Cheers,
-Brian