BAC-582: Special:Upload: Unable to load file in IE10

Apply a fix from Mediawiki 1.20

@see https://github.com/wikimedia/mediawiki-core/commit/8b73ea5f8ebe5e6da5d5e5f58363ad55cf2935aa
Merge pull request #1242 from Wikia/bac-582-upload-ie10-fix

BAC-582: Special:Upload: Unable to load file in IE10