Add null check before adding iface to pointer vector

If there is a failure in nan iface creation, nullptr is being
added to iface vector which is further leading to nullptr dereference
while iterating over the vector. Avoid adding nullptr to vector
if the iface creation fails. Also, add null check to pointer
before dereferencing it.

Bug: 356562924
Test: m
Change-Id: Ic0995aba592720f26a23d27b4e9387ab3dc86c7d
Signed-off-by: Manaswini Paluri <quic_mpaluri@quicinc.com>