Ruby

merge revision(s) 77596fb7a91cc119b25ac9e19b3c8682709765b4: [Backport #16138]

 Do not turn on keyword_init for Struct subclass if keyword hash is empty This was accidentally turned on because there was no checking for Qundef. Also, since only a single keyword is currently supported, simplify the rb_get_kwargs call. 

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_2_5@67866 b2dd03c8-39d4-4d8f-98ff-823fe69b080e