Make sure signalLater isn't called in addLineWidget when there's no editor
Make sure signalLater isn't called in addLineWidget when there's no editor

Closes #5221

dperetti/CodeMirror,namin/CodeMirror,wingify/CodeMirror,mtaran-google/CodeMirror,dperetti/CodeMirror,wingify/CodeMirror,jkaplon/CodeMirror,codio/CodeMirror,SidPresse/CodeMirror,thomasjm/CodeMirror,hackmdio/CodeMirror,ficristo/CodeMirror,nightwing/CodeMirror,hackmdio/CodeMirror,pabloferz/CodeMirror,jkaplon/CodeMirror,SidPresse/CodeMirror,ficristo/CodeMirror,hackmdio/CodeMirror,notepadqq/CodeMirror,mtaran-google/CodeMirror,pabloferz/CodeMirror,nightwing/CodeMirror,namin/CodeMirror,thomasjm/CodeMirror,notepadqq/CodeMirror,ficristo/CodeMirror,dperetti/CodeMirror,codio/CodeMirror,SidPresse/CodeMirror,nightwing/CodeMirror,namin/CodeMirror,notepadqq/CodeMirror,mtaran-google/CodeMirror,pabloferz/CodeMirror,jkaplon/CodeMirror,thomasjm/CodeMirror,wingify/CodeMirror,codio/CodeMirror