gril: fix emulator SIM IO crash (LP: #1268743)

The Touch emulator can return a SIM IO response
with a null response field.  This was being treated
as a valid reply, which could cause the code SIM code
to crash in sim_adn_parse().
unit: add unit test for SIM IO fix (LP: #1268743)

Add a unit test to verify that SIM responses with
null response are treated as an invalid reply.