Commit d2c6ad672 for imagemagick.org

commit d2c6ad672edf0a89ec4c5b698ac0af8169923dc3
Author: Cristy <mikayla-grace@urban-warrior.org>
Date:   Tue Jan 12 19:06:30 2021 -0500

    ...

diff --git a/MagickCore/compare.c b/MagickCore/compare.c
index 79f101c9b..64915c873 100644
--- a/MagickCore/compare.c
+++ b/MagickCore/compare.c
@@ -1614,7 +1614,7 @@ MagickExport MagickBooleanType GetImageDistortion(Image *image,
   /*
     Get image distortion.
   */
-  length=MaxPixelChannels+1;
+  length=MaxPixelChannels+1UL;
   channel_distortion=(double *) AcquireQuantumMemory(length,
     sizeof(*channel_distortion));
   if (channel_distortion == (double *) NULL)