gdk3: fix RG_DEF_METHOD
gdk3: fix RG_DEF_METHOD

Because it should be pass -1 into RG_DEF_METHOD's second argument, when
defined method takes variable length argument.

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