Bug: expand autocmd with <abuf> is wrong for BufUnload

[chemzqm]

  @Autocmd('BufUnload', {
    sync: true,
    pattern: '*',
    eval: 'expand("<abuf>")'
  })
  public async onBufUnload(bufnr: string):Promise<void> {
    logger.debug(`file: ${bufnr} remove`)
  }

The bufnr here is always the buffer number of current buffer number, but it should be the buffer number of removed buffer.

autocmd BufUnload * call s:OnUnload()
function! s:OnUnload()
  echo +expand('<abuf>')
endfunction

vim script doesn't have this problem.

BTW: <afile> is neither correct.

[chemzqm]

I've changed to use latest master branch. Issue still exists, but it only occurs when delete hidden buffer, the buffer number would always be current buffer number.