gdk-wayland backend would not re-configure a surface when its size and
scale match the known size and scale.
But there might be a pending xdg_surface_configure() that would revert
this change so we should re-configure even if the currently known
size/scale match, otherwise we may end up with a wrong size after the
xdg_surface_configure() is received.
Bugzilla: https://bugzilla.gnome.org/show_bug.cgi?id=758901
f37aa415cd