Fix another GtkFixed regression, in gtk_fixed_forall()
Fix another GtkFixed regression, in gtk_fixed_forall()

b3f6f67c changed the loop from while() to for() in gtk_fixed_forall(),
but that's wrong since the callback can have side-effects on the list,
in case the current child gets removed. And that's the case when the
widget is destroyed.

Patch by Vincent Untz
https://bugzilla.gnome.org/show_bug.cgi?id=641196

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