I noticed this error while working on MDL-35928.

When filepicker modal is open and session has timeout, selecting repository such as 'private file' doesn't force the page to redirect to login page.

I think when session had timed out, filepicker modal shouldn't be accessible at all.

Steps to reproduce:

1. Login as a student
2. Navigate to a course
3. Click the assignment
4. Click add..
5. Select any repository except 'private files'
6. Leave it open until session time out. (as admin, set '$CFG->sessiontimeout = 0.1;' in config.php to make the session time out immediately)
7. Click the Private files button in the file picker

It displays a pop up message containing script has been terminated.