Fix device name string on output switcher chip

The output switcher chip should show a default 'Other Device' string when we do
not have reliable device info to show. However MediaDeviceManager was always
using the local device name, and MediaControlPanel never actually used the
fallback string.
This sets the device name to null when it is untrusted, and fixes MCP to show
the fallback value in that case.

Fixes: 240185112
Test: atest MediaDeviceManagerTest MediaControlPanelTest
Test: manual (see bug)
Change-Id: I4135b6bedb7f1780e2068673e8980bf7f7b14015