bluetooth: fix crash on accessing null adapter

By checking bluetooth adaptor before accessing it,
because it could be null on devices that do not
support bluetooth, such as android emulator.

BUG: 121129248

Test:
lunch sdk_gphone_x86-userdebug
make -j
emulator
launch chrome and it should not crash

Change-Id: Ia75b5ee1efa3a8195056dada079239931eb9d901