encoding.c: new termlen not oldtermlen

* encoding.c (rb_enc_associate_index): fill new terminator length, not
  old one.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@41937 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
* properties.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@41938 b2dd03c8-39d4-4d8f-98ff-823fe69b080e