Removing Backlog without toggling off Epic Panel in Kanban Board hides Epics

Issue Summary

Steps to Reproduce

1. Create a Kanban Board;
2. Create an Epic;
3. Epic should appear in the Kanban Board;
4. Access Board Settings;
5. Map the Epic status in Backlog and toggle on the Epic Panel;
6. Epic should appear in the Backlog Epic Panel;
7. Remove Backlog by mapping the status in another column;
8. Epic won't show in the board anymore.

Expected Results

When unmapping all statuses from Backlog the Epic Panel should automatically be toggled off, since it's a Backlog only feature.

Actual Results

If all statuses are unmapped from the Backlog before toggling off the Epic Panel, Epics won't be shown in the Kanban Board.

Workaround

Map a status where there are Epics in the Backlog and toggle off the Epic Panel, then map the status again to the right Column.