cmocka: Allow test_free() to deal with NULL pointers.
cmocka: Allow test_free() to deal with NULL pointers.

Signed-off-by: Andreas Schneider <5be00ddc76278cf6077f5047ca3384a88460c671@cryptomilk.org>

jamesmunns/CMocka,jhrozek/cmocka,clibs/cmocka,wingyplus/cmocka,jhrozek/cmocka,jhrozek/cmocka,tyc/cmocka,dsch/cmocka,wingyplus/cmocka,tyc/cmocka,VladimirTyrin/cmocka,JonathonReinhart/cmocka,VladimirTyrin/cmocka,jamesmunns/CMocka,clibs/cmocka,tyc/cmocka,dsch/cmocka,JonathonReinhart/cmocka