Fix race condition with polling when saving notes

eTagPoll may not be initialized yet when we save a note.
Polling is initialized only after discussions are loaded

app/assets/javascripts/notes/stores/actions.js

@@ -357,11 +357,11 @@ export const poll = ({ commit, state, getters, dispatch }) => {
 };
 
 export const stopPolling = () => {
-  eTagPoll.stop();
+  if (eTagPoll) eTagPoll.stop();
 };
 
 export const restartPolling = () => {
-  eTagPoll.restart();
+  if (eTagPoll) eTagPoll.restart();
 };
 
 export const fetchData = ({ commit, state, getters }) => {

changelogs/unreleased/fix-comment-race-condition.yml

@@ -0,0 +1,5 @@
+---
+title: Fix commenting before discussions are loaded
+merge_request: 30724
+author:
+type: fixed