Bug 1972773 - avoid showing "confirm quit" dialog in Content Analysis if we have already cancelled quit a=diannaS

I think there may be some other corner cases (if the user decides to confirm
the quit with a download running we still still show a dialog here), but
that is harder to fix and this is a start.

Original Revision: https://phabricator.services.mozilla.com/D254291

Differential Revision: https://phabricator.services.mozilla.com/D258213

browser/components/contentanalysis/content/ContentAnalysis.sys.mjs

@@ -215,6 +215,11 @@ export const ContentAnalysis = {
   async observe(aSubj, aTopic, _aData) {
     switch (aTopic) {
       case "quit-application-requested": {
+        if (aSubj.data) {
+          // something has already cancelled the quit operation,
+          // so we don't need to do anything.
+          return;
+        }
         let pendingRequestInfos = this._getAllSlowCARequestInfos();
         let requestDescriptions = Array.from(
           pendingRequestInfos.flatMap(info =>