Fix RHS not closing when thread is deleted by another user (#3641)

webapp/actions/websocket_actions.jsx

@@ -159,6 +159,11 @@ function handlePostEditEvent(msg) {
 function handlePostDeleteEvent(msg) {
     const post = JSON.parse(msg.data.post);
     GlobalActions.emitPostDeletedEvent(post);
+
+    const selectedPostId = PostStore.getSelectedPostId();
+    if (selectedPostId === post.id) {
+        GlobalActions.emitCloseRightHandSide();
+    }
 }
 
 function handleNewUserEvent() {