range.c: return nil for empty range
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@42407 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
range.c: return nil for empty range
predecessor is smaller than the begin. [Bug #8739]
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@42407 b2dd03c8-39d4-4d8f-98ff-823fe69b080e