AudioService: fix wakelock when BT profile proxy is null

When the BT service communicates that a new BT device is active,
and the corresponding profile proxy for BT is null (bug),
the wakelock for the message handling wasn't released.

Bug: 319128812
Test: adb shell dumpys audio | grep "\- STREAM_MUSIC:" -A2
Change-Id: Iaa9e8338d99d1f897444d6246f415104bd78350b