follow GKeyFile behavior change for empty file since GLib 2.31.2.
follow GKeyFile behavior change for empty file since GLib 2.31.2.

GitHub: fixes #66

Reported by mtasaka. Thanks!!!

kitachro/ruby-gnome2,kitachro/ruby-gnome2,kitachro/ruby-gnome2,kitachro/ruby-gnome2,kitachro/ruby-gnome2