Resolve "Sort updated comments chronoligically"

Closes #167 (closed)

frontend/src/components/submission_notes/SubmissionCorrection.vue

@@ -171,6 +171,7 @@ export default {
       }, 5e3)
     },
     getSortedComments (lineNo) {
+      if (!this.origFeedback || (!this.origFeedback && !this.origFeedback[lineNo])) return new Array()
       let feedback = [...this.origFeedback[lineNo]]
 
       return feedback.sort((a, b) => {