NULL pointer should be checked before any dereference.  This patch
move memest after the NULL pointer check.

Signed-off-by: Prabhakar Kushwaha <prabhakar.kushwaha@nxp.com>
Reported-by: Jose Rivera <german.rivera@nxp.com>
Acked-by: Joe Hershberger <joe.hershberger@ni.com>
Reviewed-by: York Sun <york.sun@nxp.com>