SpatializerHelper: fix canBeSpatializedOnDevice NPE

Check whether routing is known when calling
canBeSpatializedOnDevice. Unknown routing is defined
by an empty list of devices for the requested
AudioAttributes.

Add test method in SpatializerHelper to force state.
Implement a unit test covering failure modes when
querying routing.

Test: atest com.android.server.audio.SpatializerHelperTest#testNoRoutingCanBeSpatialized
Bug: 267963974
Change-Id: Ib6d73fec4d57cf372361762b5c1d85329794de92