Issue Summary

Using files with a `+` in the filename as attachment fail to be displayed correctly on Public Boards.

Example: https://trello.com/b/uZDV6SYQ/public-board

See the first two cards on the "List 1"

Steps to Reproduce

1. Create two boards, one org visible and one public

1. On the org visible board, create a card and attach an image with the name `test+image`

1. Transfer the card to your public board.

1. Click on the attachment to open it

Expected Results

The attachment opens without errors

Actual Results

The attachment fails to open.

Workaround

Rename files with `+` in the filename before using them an attachment to be used in a public board.