Gio::FileInfo::list_attributes(): Make name_space optional.
Gio::FileInfo::list_attributes(): Make name_space optional.

Because I noticed that this has just been documented as being allowed
to be null:
https://git.gnome.org/browse/glib/commit/?id=a4ed89bf75190631087596be22f9eb10dc6e53ef

GNOME/glibmm,GNOME/glibmm,GNOME/glibmm,GNOME/glibmm,GNOME/glibmm