diag: Add NULL pointer checks for mask info

Currently there is a possibility of NULL pointer
dereference issue due to NULL pointers checks are
missing for mask info. The patch fixes the issue by
adding NULL pointer checks.

CRs-Fixed: 2108911
Change-Id: I097aeacc90c8d88034bf799ee4e398ddda5e23f1
Signed-off-by: Hardik Arya <harya@codeaurora.org>