Scrolling when cursor is on the first line

When the cursor is on the first line in the main buffer and scrolloff=0, opening fzf causes the main buffer to scroll down by a single line.

I believe the problem is the line

    execute 'normal! '.(topWinLine + &scrolloff - 1).'jzt'

which evaluates to 0j, which (counter-intuitively) seems to be equivalent to 1j.

Thanks for the awesome plugin!