src: Make sure the iterator is inbound before decrementing it
src: Make sure the iterator is inbound before decrementing it

Fixes #2966

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