rc modeline: Don't select more lines than configured
rc modeline: Don't select more lines than configured

This commit addresses an off-by-one error that selected `modelines`+1
lines when looking for modelines in a buffer.

Note that setting `modelines` to 0 will still select one line.

Fixes #3733.

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