bug#38181: Actual height of mode-line not taken into account

[Carlos Pita]

In practice this seems to nicely cover the relevant cases:

(defun my-redisplay-hack (&rest _)
  (when mode-line-format
    (redisplay t)))
(advice-add #'split-window :after #'my-redisplay-hack)

but there is some flickering because the window is displayed before
the fit and then immediately replaced by the fitted version. Although
I see no way around that glitch, so it might be the price to pay.