HFP: AG: Add null check for AdapterService

When BT is turned off, mAdapterService will be
set to null. At the same time, if a headset gets
disconnected, mAdapterService is dereferenced
without null check to send disconnected intent.
Add the null check for mAdapterService while
getting the bonded devices.

CRs-Fixed: 2486935
Change-Id: Id8dbcbabe4faeb8fcf3cbf31573422da38cb03a2
1 file changed