py/stream: ioctl(): Properly support 2-arg form.

py/stream.c

@@ -414,13 +414,15 @@ STATIC mp_obj_t stream_ioctl(size_t n_args, const mp_obj_t *args) {
     const mp_stream_p_t *stream_p = mp_get_stream_raise(args[0], MP_STREAM_OP_IOCTL);
 
     mp_buffer_info_t bufinfo;
-    uintptr_t val;
+    uintptr_t val = 0;
+    if (n_args > 2) {
         if (MP_OBJ_IS_INT(args[2])) {
             val = mp_obj_get_int(args[2]);
         } else {
-        mp_get_buffer_raise(args[2], &bufinfo, MP_BUFFER_READ);
+            mp_get_buffer_raise(args[2], &bufinfo, MP_BUFFER_WRITE);
             val = (uintptr_t)bufinfo.buf;
         }
+    }
 
     int error;
     mp_uint_t res = stream_p->ioctl(args[0], mp_obj_get_int(args[1]), val, &error);