Warn when calling gtk_window_parse_geometry() on an empty window
Warn when calling gtk_window_parse_geometry() on an empty window

gtk_window_parse_geometry() gets the size of the window in order
to interpret the position of the window; calling it before, say,
calling gtk_widget_show_all() on a window is a subtle trap, so
add a warning in the case we can easily detect.

https://bugzilla.gnome.org/show_bug.cgi?id=631794

bratsche/gtk-,Sidnioulz/SandboxGtk,davidt/gtk,chergert/gtk,alexlarsson/gtk,alexlarsson/gtk,ahodesuka/gtk,msteinert/gtk,jadahl/gtk,jadahl/gtk,davidt/gtk,davidgumberg/gtk,jigpu/gtk,alexlarsson/gtk,msteinert/gtk,Lyude/gtk-,jessevdk/gtk,Distrotech/gtk2,chergert/gtk,chergert/gtk,simokivimaki/gtk,alexlarsson/gtk,ahodesuka/gtk,ahodesuka/gtk,Lyude/gtk-,ahodesuka/gtk,chergert/gtk,Lyude/gtk-,Sidnioulz/SandboxGtk,jessevdk/gtk,alexlarsson/gtk,Adamovskiy/gtk,simokivimaki/gtk,davidt/gtk,jadahl/gtk,Distrotech/gtk2,davidgumberg/gtk,grubersjoe/adwaita,davidgumberg/gtk,jessevdk/gtk,Adamovskiy/gtk,Adamovskiy/gtk,Adamovskiy/gtk,davidgumberg/gtk,ebassi/gtk,msteinert/gtk,davidgumberg/gtk,simokivimaki/gtk,chergert/gtk,jigpu/gtk,jessevdk/gtk,Sidnioulz/SandboxGtk,jadahl/gtk,Adamovskiy/gtk,jigpu/gtk,davidt/gtk,bratsche/gtk-,grubersjoe/adwaita,jadahl/gtk,grubersjoe/adwaita,Lyude/gtk-,ebassi/gtk,msteinert/gtk,bratsche/gtk-,msteinert/gtk,bratsche/gtk-,jadahl/gtk,jigpu/gtk,ahodesuka/gtk,Lyude/gtk-,davidt/gtk,simokivimaki/gtk,jessevdk/gtk,grubersjoe/adwaita,ahodesuka/gtk,ebassi/gtk,Distrotech/gtk2,ahodesuka/gtk,jadahl/gtk,jadahl/gtk,alexlarsson/gtk,ahodesuka/gtk,alexlarsson/gtk,bratsche/gtk-,alexlarsson/gtk,Adamovskiy/gtk,jessevdk/gtk,simokivimaki/gtk,chergert/gtk,jigpu/gtk,grubersjoe/adwaita,Lyude/gtk-,Adamovskiy/gtk,Sidnioulz/SandboxGtk,davidt/gtk,jigpu/gtk,jigpu/gtk,simokivimaki/gtk,ebassi/gtk,msteinert/gtk,bratsche/gtk-,Distrotech/gtk2,grubersjoe/adwaita,Distrotech/gtk2,grubersjoe/adwaita,davidgumberg/gtk,Sidnioulz/SandboxGtk,Sidnioulz/SandboxGtk,chergert/gtk,jigpu/gtk,Lyude/gtk-,Lyude/gtk-,Distrotech/gtk2,ebassi/gtk,Adamovskiy/gtk,jessevdk/gtk,grubersjoe/adwaita,chergert/gtk,davidgumberg/gtk,davidgumberg/gtk,ebassi/gtk