tests: Reset output buffer in torture_crypto

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

tests/unittests/torture_crypto.c

@@ -84,6 +84,7 @@ static void torture_crypto_aes256_cbc(void **state)
             iv
     );
 
+    memset(output, '0', sizeof(output));
     cipher.decrypt(&cipher,
             aes256_cbc_encrypted,
             output,