Fixes keywords are lost with the `OP_SENDB`
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>]
```
@@ -1573,7 +1573,7 @@ RETRY_TRY_BLOCK:
mrb_value recv;
if (0 < nk && nk < 15) { /* pack keyword arguments */
- mrb_int kidx = a+n+1;
+ mrb_int kidx = a+(n==15?1:n)+1;
mrb_value kdict = hash_new_from_values(mrb, nk, regs+kidx);
regs[kidx] = kdict;
nk = 15;
