GHSA-CJC8-G9W8-CHFW imagemagick: heap-buffer overflow read in MNG magnification with alpha

Vulnerability Details When performing image magnification in ReadOneMNGIMage in coders/png.c, there is an issue around the handling of images with separate alpha channels. When loading an image with a color type that implies a separate alpha channel ie. jngcolortype = 12, we will load the alpha...