string.c: skip invalid char gap
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@54210 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
string.c: skip invalid char gap
gap between GREEK CAPITAL RHO and SIGMA.
[ruby-core:74478] [Bug #12204]
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@54210 b2dd03c8-39d4-4d8f-98ff-823fe69b080e