Displaying just one column means pages are arranged vertically

Displaying just one column means pages are arranged vertically

Third-party display methods may do that without using a side-window,
and therefore they don't set `which-key-popup-type' to `side-window'.
Likewise they might not set `which-key-side-window-location', e.g.,
because their display method only supports one location.

`which-key-max-display-columns' being 1 is by itself already enough
of an indicator to know that there won't be multiple columns.