Fixed file extension when downloading a single IFS file

[sebjulliand]

Changes

When downloading a single IFS file, the extension in the File selection dialog is not right (it starts with .) and the dialog doesn't show the files with this extension:

This PR removes the . in the extension name and fixes this issue:

How to test this PR

1. With version 2.8.0: try downloading a single file from the IFS browser: extension is wrong, no existing files with the extension are shown.
2. With the PR checked out: try downloading a single file from the IFS browser: extension is OK, files with the same extension in the folder are shown.

Checklist

• have tested my change

[worksofliam]

Tested on Mac and it continued to work good before and after.