window-text-pixel-size and presumable move_it_to change(s)

[martin rudalics]

‘fit-window-to-buffer’ is currently broken on master when the window is
horizontally combined.  I traced it back to the following differnece:
Consider these two forms:

(window-text-pixel-size nil (window-start) (point-max) (frame-pixel-width) 
(window-body-height nil t))

(window-text-pixel-size nil (window-start) (point-max) nil (window-body-height 
nil t))

With emacs -Q on the release branch evaluating both forms via M-: gets
me (576 . 48).

With emacs -Q on master evaluating the first form gets me (0 . 48) while
evaluating the second form gets me (576 . 48).  I conclude that the
behavior of move_it_to has changed recently when setting

      it.last_visible_x = max_x;

in Fwindow_text_pixel_size.  Is that conclusion correct?  If so, what
can I do to get the old behavior back?

Thanks, martin