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
(cherry picked from commit 7d7222c3e5c1054b4e2f3e59cc40cb182a72b040)
(cherry picked from commit 8ce523155dd030d82c32cf502d317023b017645b)
(cherry picked from commit 938686e749bca911e5f63150223116d1c381da8e)