Fix IAE for bluetooth routes without set BT address

This change just adds a last resort check to avoid the exception and fix
the crash. Further checks will be added in the routing framework to avoid
this incongruent state.

Test: atest com.android.settingslib.media and manually with demo app
Bug: 347499404
Flag: EXEMPT bugfix
Change-Id: I87e6810467bcae0bac7f0418217b03e57c1d8c03