iconview: gtk_icon_view_compute_n_items_for_size bugfix
iconview: gtk_icon_view_compute_n_items_for_size bugfix

While working on the "iconview: Don't shrink items" patch I noticed that
gtk_icon_view_compute_n_items_for_size modifies the natural and minimum
item sizes it got from gtk_icon_view_get_preferred_item_size when
calculating the max number of items which will fit, but later on it
checks against these sizes when calculating the item_size, and these
checks expect these values to be unmodified.

This patch fixes this by modifying the natural and minimum values in
advance and doing all computations with modified values.

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

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