2D Recents: Fix issue with undocking only one task

While there's only one task and we undock it, it's not in the Recents
task list. In this change, we just reset the transform and return it.

Test: Checked that Recents works properly while docking and undocking a
task and it's the only task running.
Bug: 32101881

Change-Id: I1207b546ff2864018c8d9bf2520f4690762b2d27