Support the case when the playing device is unknown in the

MediaOutputComponent.

This happens for a remote session when the app doesn't provide the
device it's casting to

Flag: EXEMPT bugfix
Fixes: 357008293
Test: atest VolumePanelScreenshotTest
Test: manual on fildable with remote tv. Cast YouTube and Spotify
content and observe Volume Panel header behaviour

Change-Id: Id702a08b2d9a798cba3c7946fafb87c784fe0145