iconview: Special case the empty iconview
iconview: Special case the empty iconview

If the icon view is empty, we cannot get a reasonable size request from
the cell renderers. So all values we would compute are pretty much
useless.
So we special case it.

This also gets rid of a bunch of crashers from div-by-0 in corner cases.

https://bugzilla.gnome.org/show_bug.cgi?id=677809

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