[comment addon] Keep selection in front of closing marker when block-commenting
[comment addon] Keep selection in front of closing marker when block-commenting

... with fullLines==false when the end of the selection is directly on the closing
marker.

Closes #6375

nightwing/CodeMirror,pabloferz/CodeMirror,pabloferz/CodeMirror,wingify/CodeMirror,pabloferz/CodeMirror,hackmdio/CodeMirror,wingify/CodeMirror,nightwing/CodeMirror,hackmdio/CodeMirror,dperetti/CodeMirror,hackmdio/CodeMirror,wingify/CodeMirror,dperetti/CodeMirror,nightwing/CodeMirror,dperetti/CodeMirror