Bug 1672778 - [devtools] Avoid trying to send new-source event if the thread actor has been destroyed. r=nchevobbe

This may prevent logging a few exception or error messages.
But thanks to the other patch of this bug, we should try to stop listening
for sources as soon as the thread actor is destroyed.

Differential Revision: https://phabricator.services.mozilla.com/D94484

devtools/server/actors/thread.js

@@ -2042,6 +2042,9 @@ const ThreadActor = ActorClassWithSpec(threadSpec, {
     // We use executeSoon because we don't want to block those operations
     // by sending packets in the middle of them.
     DevToolsUtils.executeSoon(() => {
+      if (this.isDestroyed()) {
+        return;
+      }
       this.emit("newSource", {
         source: source.form(),
       });