Crashes on indexed images.

It crashes on indexed images. I believe the issue lies here in Encode(Bitmap b, float quality, out IntPtr result, out long length)
using (Bitmap b2 = b.Clone(new Rectangle(0, 0, b.Width, b.Height), System.Drawing.Imaging.PixelFormat.Format32bppArgb))
{
Encode(b2, quality, out result, out length);
}
I've created a workaround that works nicely which is
if (b.PixelFormat.HasFlag(PixelFormat.Indexed))
{
using (var bitmap = new Bitmap(b.Width, b.Height, PixelFormat.Format32bppArgb))
{
using (var graphics = Graphics.FromImage(bitmap))
{
graphics.DrawImageUnscaled(b, 0, 0, b.Width, b.Height);
}
//this is using the stream to. it would have to be revised to reflect your out params
Encode(bitmap, to, quality);
}
}

Start at Encode(Bitmap b, float quality, out IntPtr result, out long length) and reproduce the crash with an indexed Bitmap. Compare that path with the provided Format32bppArgb conversion workaround. Done means indexed images encode without crashing and existing image encoding still works.

Written by the indexing model from the issue text.