Avoid a DOS in vision.c due to an infinite loop. CVE assignment: http://seclists.org/oss-sec/2016/q2/459 Patch: https://anonscm.debian.org/cgit/collab-maint/imagemagick.git/commit/?h=debian-patches/6.8.9.9-4-for-upstream&id=c504b8e1a1ca6f158f2d08bd33c62ce4865497ee