merge revision(s) 62040: [Backport #14388]
string.c: clear substring code range * string.c (str_substr): substring of broken code range string may be valid or broken. patch by tommy (Masahiro Tomita) at [ruby-dev:50430] [Bug #14388].
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_2_5@62483 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
merge revision(s) 62040: [Backport #14388]
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_2_5@62483 b2dd03c8-39d4-4d8f-98ff-823fe69b080e