Fix an error when calling a method implemented in C by super() with argu...

This PR fixes an error when calling a method implemented in C by super() with some arguments .
It makes the following code workable:

Expected:

~~~~
class MRBTime < Time; def self.new; super(2012, 4, 21); end; end
MRBTime.new # => Sat Apr 21 00:00:00 2012
~~~~

Actual:

~~~
class MRBTime < Time; def self.new; super(2012, 4, 21); end; end
MRBTime.new # => can't convert nil into Integer (TypeError)
~~~