compile.c: no keyword check if kw_rest

* compile.c (iseq_set_arguments): no keyword check if any keyword rest
  argument exists, even unnamed.  [ruby-core:52744] [Bug #7922]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@39444 b2dd03c8-39d4-4d8f-98ff-823fe69b080e