* include/ruby/ruby.h (rb_scan_args_trail_idx): fix the case both
  of optional and rest arguments are defined.
  [ruby-core:82427] [Bug #13830]

* include/ruby/ruby.h (rb_scan_args_n_trail): ditto.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@59624 b2dd03c8-39d4-4d8f-98ff-823fe69b080e