fix error with double HID response

ctap.c

@@ -763,7 +763,7 @@ void ctap_make_credential(CborEncoder * encoder, uint8_t * request, int length)
 
     printf("der sig [%d]: ", sigder_sz); dump_hex(sigder, sigder_sz);
 
-    ctap_add_attest_statement(&map, sigder, sigderlen);
+    ctap_add_attest_statement(&map, sigder, sigder_sz);
 
     ret = cbor_encoder_close_container(encoder, &map);
     check_ret(ret);

ctaphid.c

@@ -185,7 +185,7 @@ static int buffer_len()
 static void ctaphid_write(CTAPHID_WRITE_BUFFER * wb, void * _data, int len)
 {
     uint8_t * data = (uint8_t *)_data;
-    if (len == 0)
+    if (_data == NULL)
     {
         if (wb->offset == 0 && wb->bytes_written == 0)
         {