Fix crash on non utf8 files trigering highlighting of backward ranges
Fix crash on non utf8 files trigering highlighting of backward ranges

Fixes #1274

jjthrash/kakoune,casimir/kakoune,mawww/kakoune,Somasis/kakoune,casimir/kakoune,alexherbo2/kakoune,lenormf/kakoune,alexherbo2/kakoune,Somasis/kakoune,casimir/kakoune,Somasis/kakoune,lenormf/kakoune,occivink/kakoune,jkonecny12/kakoune,danr/kakoune,Somasis/kakoune,jkonecny12/kakoune,occivink/kakoune,casimir/kakoune,occivink/kakoune,jkonecny12/kakoune,alexherbo2/kakoune,mawww/kakoune,jjthrash/kakoune,lenormf/kakoune,danr/kakoune,danr/kakoune,lenormf/kakoune,jkonecny12/kakoune,occivink/kakoune,mawww/kakoune,danr/kakoune,alexherbo2/kakoune,mawww/kakoune,jjthrash/kakoune,jjthrash/kakoune