Bluetooth: Add NULL checks for vendor block

This patch adds null checks before accessing the irk_list
pointer of the vendor capabilities block to prevent access
to the unalocated memory buffer

CRs-Fixed: 727749
Change-Id: Ib3623f0d1a7679301b54597109f5e8ab09d1636f
Conflicts:
vnd/ble/vendor_ble.c
1 file changed