Fix for false security exception

Security exceptions would be raised for file names with a "%20" in them. This is because it is also a url-encoding for the "space" character.

This means if a user uploads a photo with the name "Aaron%20Rosenzweig.jpg" then when we try to download it with ERAttachment we will receive a security exception without this fix in place. 

Signed-off-by: Aaron Rosenzweig <aaron@chatnbike.com>