Fix recents button not navigating to Overview

This CL prevents returning launcher in getVisibleLauncher method when isHomeVisible is true but Launcher is not started.

Bug: 337954957
Bug: 331947116
Flag: EXEMPT bugfix
Test: Manual. With 3-button-nav. Open a video from -1 scren (not in Youtube app), press recent button. More instructions in b/337954957#comment26.
Change-Id: I40edafdab5457666474de2c0368158a9c1c05fb0