Mapping `<Plug>(cokeline-focus-*)` doesn't work for unlisted buffers

[EtiamNullam]

Mappings <Plug>(cokeline-focus-next) and <Plug>(cokeline-focus-prev) won't switch buffer when executed from an unlisted buffer.

If buffer is listed by set buflisted or lua vim.o.buflisted = true then it will work again (for this buffer).