Scrolling sidebar file tree includes extra whitespace at the bottom

Issue Summary

On PR with a lot of files, the file tree in the sidebar has a lot of extra whitespace on the bottom of the page that a user is able to keep scrolling through.

This is reproducible on Data Center: no

Steps to Reproduce

1. Go to a PR with >100 files
2. Click the "Files" tab in the right sidebar
3. Use mouse to scroll to bottom

Expected Results

There would be no extra whitespace (not scrollable past bottom of list)

Actual Results

There is lots of extra whitespace (as much as the full file diff would have been if it wasn't in single file mode).

Workaround

None (this is only a visual bug, does not block functionality)