Throw exceptions if obtain ActivityStarter before system ready

RWC was null while starting home activity during system boot up.
Throw exceptions now if that happens again.

Also add warning logs if any unknown failures during ATM#onTransact.

Bug: 174713714
Bug: 173221781
Test: build and run
Change-Id: I5f3414d98198144af7bc0a07c7dbfafd529790e8