mount-operation: don't show the dialog until the tree is populated
mount-operation: don't show the dialog until the tree is populated

Otherwise it won't show up properly, and GTK+ will trigger a warning.
Don't know why this did not show up before.

https://bugzilla.gnome.org/show_bug.cgi?id=640744

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