[audio] Fix caching failed product strategy call

Prevent AudioService from caching a empty list when getting the product
strategy from audioserver fails. Instead, cache the first successful
call.

Some minor code quality fixups as well.

Test: boot, manual verification of call
Bug: 357468728
Flag: EXEMPT bugfix
Change-Id: I143a5b5292c1a8370e92f303ba0f6853d2ae8a37