Edited Issue: Different result .Clip() with 502 vs. 901 [1153]

Hello,

Seems like the .Clip() method behaves very odd in some cases since the 901 release.

File to reproduce with: http://download.bkbone.nl/ClipProblem.tif

Narrowed it down to:

```
using (MagickImage img = new MagickImage(@"C:\Temp\ClipProblem.tif"))
{
img.ColorSpace = ColorSpace.sRGB;
img.ColorType = ColorType.TrueColorMatte;

img.BackgroundColor = new MagickColor(0.0F, 0.0F, 0.0F, 0.0F);
img.FillColor = new MagickColor(0.0F, 0.0F, 0.0F, 0.0F);

img.Clip("Pad A", false);

img.Negate(Channels.Alpha);
img.ColorAlpha(img.FillColor);

img.Format = MagickFormat.Png24;

img.Write(@"C:\Temp\ClipProblem.png");
}
```

Result with Magick.NET x86 6.8.7.502 (Q16):
http://download.bkbone.nl/ClipProblem6.8.7.502.png
(which is fine)

Result with Magick.NET x86 6.8.7.901 (Q16):
http://download.bkbone.nl/ClipProblem6.8.7.901.png
(which is unexpected)

(Please note the alpha channel / background transparency, which may not be visible directly in some browsers, as it just appears white).

Thanks for your time!

Kindest regards,
René