gril: cleanup parse SIM IO reply (LP: #1268743)

Minor cleanup of g_ril_reply_parse_sim_io() as
part of fix for crash when a SIM IO request is
returned with a null response field.  This
change adds a malformed check, and also fixes
a leak, ensuring the response is always freed.
unit: extend grilreply SIM IO tests (LP: #1268743)
rilmodem: fix crash SIM IO crash (LP: #1268743)

The touch emulator can return responses to SIM IO
commands with a null response field.  This can cause
a crash in the core function sim_adn_parse().  So
in ril_file_io_cb() return a callback failure if
the response length is zero.