Description of problem:
If the user types an incorrect filename into the glossary upload file selector, the browser ends up on an invalid page

Version-Release number of selected component (if applicable):
3.4

How reproducible:
Easy always

Steps to Reproduce:
1. Sign in as admin, click Glossary
2. Click Upload, then Choose File
3. enter a false filename into the selector, press Open
4. Press Upload

Actual results:
Browser shows "This web page has not been found"

Expected results:
Some kind of "invalid file" error in notification

Additional info:
Tested in Chrome. Firefox simply says "Glossary file sdfsdfsdfsf.po uploaded." without actually doing anything.