Bluetooth: Security: Add Null check during pairing cancel intent.

Added null check, so before posing event we can restrict events,
if cached device list is empty

Change-Id: I458d181abe5eec2497b80b1713ddbc3502b79786
CRs-Fixed: 546364
Merge "Bluetooth: Security: Add Null check during pairing cancel intent." into jb-mr2