Throw if AOHD is inited without a underlying DSP

This prevents an intermediate state where a AlwaysOnHotwordDetector is
initialized, but doesn't have an underlying session to connect to.

Throw IllegalStateException if VIS creates an AOHD when no module
exists.

Bug: 272147641
Fixes: 269165460
Test: CtsVoiceInteractionTestCases
Test: Manual verification of hotword
Change-Id: I1e3d448fbb3e100fd963cc704397a409a4d8b8f0