Fix setting a prefix list option with an empty list
Fix setting a prefix list option with an empty list

Fixes #2335

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