This fixes CVE-2021-31810.
Reported by Alexandr Savca.

Co-authored-by: Shugo Maeda <shugo@ruby-lang.org>


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_2_6@67949 b2dd03c8-39d4-4d8f-98ff-823fe69b080e