fix non-ascii attachment file name get corrupted in IE11 (#16711)

Contributed by Go MAEDA.

git-svn-id: http://svn.redmine.org/redmine/trunk@13101 e93f8b46-1217-0410-a6f0-8f06a7374b81
Merge pull request #1175 from marutosi/finn-ie11

fix non-ascii attachment file name get corrupted in IE11 (#16711)