parse.y: attrset from junk ID

* parse.y (IDSET_ATTRSET_FOR_INTERN): fix off-by-one bug.
* parse.y (rb_enc_symname_type): junk ID succeeded by '=' is also
  attrset ID.  [ruby-core:60668] [Bug #8756]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@44926 b2dd03c8-39d4-4d8f-98ff-823fe69b080e