Display sub-task under an epic swimlane if a parent issue is hidden.

Sub-tasks should be shown on the epic swimlanes if the parent issue is hidden by a quick filter.
Use case:

1. Assign parent issues to an epic.
2. Create sub-task on a parent issues.
3. Add parent issue to an active sprint
4. Configure scrum board for epic swimlanes
5. Add quick filter that hides the parent issues but does not hide the sub-task.
6. Go to work mode and apply the quick filter from step 5.

Result: sub-task is displayed on a swimlane "Issues without an epic"
Expected result: sub-task must be shown on the epic swimlane from the parent issue. The Epic swimlane remains visible after applying the quick filter.