sprintf.c: unnumbered asterisk with numbered argument

* sprintf.c (GETASTER): should not use the numbered argument to be
  formatted, raise ArgumentError instead.
  [ruby-dev:48330] [Bug #9982]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@46569 b2dd03c8-39d4-4d8f-98ff-823fe69b080e