Avoid a SIGABRT in sun file handling
This is a partial fix for malformed sun file
Bug: http://www.imagemagick.org/discourse-server/viewtopic.php?f=3&t=26857
Bug-debian: https://bugs.debian.org/823750
Origin: upstream,
https://github.com/ImageMagick/ImageMagick/commit/1aa0c6dab6dcef4d9bc3571866ae1c1ddbec7d8f
