Optimize the empty Nary case.
Optimize the empty Nary case.

	* src/runner/interpreter-visit.hxx (visit(const ast::Nary*)):
	Optimize the empty Nary case, which is strictly equivalent
	to "void".

urbiforge/urbi,aldebaran/urbi,urbiforge/urbi,urbiforge/urbi,aldebaran/urbi,urbiforge/urbi,aldebaran/urbi,aldebaran/urbi,urbiforge/urbi,urbiforge/urbi,aldebaran/urbi,urbiforge/urbi,aldebaran/urbi,aldebaran/urbi,aldebaran/urbi,urbiforge/urbi,urbiforge/urbi