If a splat argument was passed, it could write out of range on the VM stack.

```console
% bin/mruby -e 'def m(*args, **opts, &blk) p [args, opts, blk] end; m(*%w(X Y Z), r: 1, g: 2, b: 3) {}'
[["X", "Y", "Z"], {}, #<Proc:0x80077d7d0>]
```