ImageMagick: Invalid MSL <map> can result in a use after free

ImageMagick is free and open-source software used for editing and manipulating digital images. Prior to versions 7.1.2-15 and 6.9.13-40, the MSL interpreter crashes when processing a invalid `<map>` element that causes it to use an image after it has been freed. Versions 7.1.2-15 and 6.9.13-40 contain a patch.