Icns DOS fix --  CVE-2014-3589

Found and reported by Andrew Drake of dropbox.com
Merge pull request #845 from wiredfool/icns_cve

Icns DOS fix --  CVE-2014-3589
Update Changes.rst [ci skip]
Updated Changes.rst [ci skip]

formatting
Merge branch 'master' of https://github.com/python-pillow/Pillow