save pane id instead of index
save pane id instead of index

pane index '#P' will change when new pane added.
Somasis/kakoune,Somasis/kakoune,lenormf/kakoune,casimir/kakoune,lenormf/kakoune,jkonecny12/kakoune,mawww/kakoune,mawww/kakoune,lenormf/kakoune,alexherbo2/kakoune,mawww/kakoune,jjthrash/kakoune,casimir/kakoune,mawww/kakoune,occivink/kakoune,jkonecny12/kakoune,jkonecny12/kakoune,casimir/kakoune,jjthrash/kakoune,danr/kakoune,occivink/kakoune,alexherbo2/kakoune,occivink/kakoune,danr/kakoune,lenormf/kakoune,Somasis/kakoune,jjthrash/kakoune,occivink/kakoune,casimir/kakoune,alexherbo2/kakoune,Somasis/kakoune,jjthrash/kakoune,danr/kakoune,alexherbo2/kakoune,danr/kakoune,jkonecny12/kakoune