Fix a outofbound access for psd file
Added extra check to fix
https://github.com/ImageMagick/ImageMagick/issues/93
origin: upstream,
https://github.com/ImageMagick/ImageMagick/commit/4b1b9c0522628887195bad3a6723f7000b0c9a58
bug: https://github.com/ImageMagick/ImageMagick/issues/93
bug-ubuntu:
https://bugs.launchpad.net/ubuntu/+source/imagemagick/+bug/1537419
bug-debian: https://bugs.debian.org/823750
