[Dual Shade] Show the notifications shade clock when the shade is empty.

Bug: 404798547
Test: Existing unit tests still pass.
Test: Manually by opening the notifications shade with and without
 notifications present, and observing that the clock is shown in both
 cases (and not shown in both cases when the device is unfolded).
Flag: com.android.systemui.scene_container
Change-Id: Ifa9272a755aef128c17d1366f0ffb9fa6d18b479