file chooser: Avoid animated scrolling for editing

file chooser: Avoid animated scrolling for editing

Avoid scrolling animation when scrolling to where we want
to insert the new folder, since adding the entry doesn't
do the right thing if the treeview is still scrolling.

An alternative would be to wait for the animated scrolling
to reach its target before starting the editing, but this
is easier.

https://bugzilla.gnome.org/show_bug.cgi?id=729366