bug#51590: Tab-line breaks windows of follow-mode

[Eli Zaretskii]

> From: Juri Linkov <juri@linkov.net>
> Date: Wed, 03 Nov 2021 20:24:18 +0200
> 
> The most low-level function of follow-mode is follow-calc-win-end.
> When global-tab-line-mode is enabled, follow-calc-win-end
> returns the same values as when global-tab-line-mode is disabled.

Can you step through that function and see which part is misbehaving
there?

> I don't understand what more low-level function doesn't take
> into account the height of the tab-line.  Maybe the problem is
> in pos-visible-in-window-p?  Or maybe different values returned
> by window-inside-pixel-edges and window-end?

I don't know the answer, but I see that header-line-format is
mentioned in one place in follow.el, and that is not a good sign...