Warning when setting the titlebar

[clayrisser]

I get the following warning when adding a HeaderBar which sets the titlebar.

(org.gnome.Cody:2): Gtk-WARNING **: 08:12:11.544: gtk_window_set_titlebar() called on a realized window

I believe this happens because the window is rendered before the titlebar is set.

[ncpa0cpl]

does this cause any issues aside from displaying a warning? because of how React works it a little bit tricky to do things in a different order, so unless there's an actual bug caused by it I don't think there's any point in fixing it