[Dual Shade] Do not show the empty state message when media is active.

Fix: 400637571
Test: NotificationListViewModelTest
Test: Manually tested by observing the notifications shade with and
 without notifications and media present, and confirming the expected
 behavior.
Flag: com.android.systemui.scene_container
Change-Id: I0f0a0f3b6639eedc56c9fcca53766afac2a5c523