Added warnings to GtkCellLayout when api is accessed and there is no GtkCellArea to operate on.
Added warnings to GtkCellLayout when api is accessed and there is no GtkCellArea to operate on.

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