Wrong link to the manual lang pack installation in 1.8 installer

Steps to reproduce
===============
1. set "allow_url_open" to 0 in your php.ini so Moodle will not be able to download lang pack automatically
2. start new installation in a non-English language
3. after "Download language pack button" stage there is a screen with a link for manual download

What I expected
=============
See links to http://download.moodle.org/lang16/cs_utf8.zip

What actually happened
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I got link with missing filename: http://download.moodle.org/lang16/.zip