GtkDialog: protect against show_all
GtkDialog: protect against show_all

The real reason for the problem that the just reverted change
was supposed to address is that testfilechooser uses show_all
to tease out places where composite dialogs don't properly
protect their internals against unintended showing. Well,
lets do that, then.

jigpu/gtk,grubersjoe/adwaita,Adamovskiy/gtk,alexlarsson/gtk,grubersjoe/adwaita,jessevdk/gtk,alexlarsson/gtk,ahodesuka/gtk,Lyude/gtk-,ahodesuka/gtk,davidgumberg/gtk,Adamovskiy/gtk,Sidnioulz/SandboxGtk,davidgumberg/gtk,grubersjoe/adwaita,Adamovskiy/gtk,grubersjoe/adwaita,ahodesuka/gtk,Adamovskiy/gtk,alexlarsson/gtk,jigpu/gtk,jessevdk/gtk,msteinert/gtk,alexlarsson/gtk,davidgumberg/gtk,Sidnioulz/SandboxGtk,jessevdk/gtk,jessevdk/gtk,Lyude/gtk-,Lyude/gtk-,chergert/gtk,Adamovskiy/gtk,msteinert/gtk,ahodesuka/gtk,alexlarsson/gtk,alexlarsson/gtk,Adamovskiy/gtk,grubersjoe/adwaita,alexlarsson/gtk,grubersjoe/adwaita,jadahl/gtk,chergert/gtk,jadahl/gtk,Lyude/gtk-,jigpu/gtk,chergert/gtk,grubersjoe/adwaita,ahodesuka/gtk,alexlarsson/gtk,jigpu/gtk,Lyude/gtk-,Adamovskiy/gtk,jigpu/gtk,Sidnioulz/SandboxGtk,Lyude/gtk-,chergert/gtk,jigpu/gtk,davidgumberg/gtk,jadahl/gtk,Adamovskiy/gtk,jessevdk/gtk,davidgumberg/gtk,jigpu/gtk,jadahl/gtk,Sidnioulz/SandboxGtk,chergert/gtk,jadahl/gtk,ahodesuka/gtk,msteinert/gtk,grubersjoe/adwaita,davidgumberg/gtk,davidgumberg/gtk,jigpu/gtk,jadahl/gtk,chergert/gtk,jadahl/gtk,msteinert/gtk,ahodesuka/gtk,Sidnioulz/SandboxGtk,chergert/gtk,Lyude/gtk-,chergert/gtk,Sidnioulz/SandboxGtk,Lyude/gtk-,davidgumberg/gtk,ahodesuka/gtk,jessevdk/gtk,jadahl/gtk,jessevdk/gtk,msteinert/gtk,msteinert/gtk