bug#46827: Broken initial size of GTK3 frame

[Robert Pluim]

>>>>> On Tue, 2 Mar 2021 10:07:02 +0100, martin rudalics <rudalics@gmx.at> said:

    >> So the problem still seems that redisplay misses a pending
    >> window change.

    martin> Confirmed meanwhile.  The attached patch fixes the problem here.  
Eli
    martin> will tell use whether we can put that do_pending_window_change in 
some
    martin> suitable safe place within redisplay_internal.

It fixes it for me as well in emacs-27 and master (and the
frame-height is correct), and doesnʼt appear to have broken anything
under Gnome.

Robert
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