[MM-60603] Don't follow threads when marking them as read on focus (#28263)

* [MM-60603] Don't follow threads when marking them as read on focus

* Fix tests

* Fix lint

* Fix the original bug in the API call

webapp/channels/src/actions/views/threads.ts

@@ -5,6 +5,7 @@ import {batchActions} from 'redux-batched-actions';
 
 import {updateThreadRead} from 'mattermost-redux/actions/threads';
 import {getCurrentTeamId} from 'mattermost-redux/selectors/entities/teams';
+import {getThread} from 'mattermost-redux/selectors/entities/threads';
 import {getCurrentUserId} from 'mattermost-redux/selectors/entities/users';
 import type {ThunkActionFunc} from 'mattermost-redux/types/actions';
 
@@ -56,8 +57,9 @@ export function markThreadAsRead(threadId: string): ThunkActionFunc<void, Global
         const state = getState();
         const currentUserId = getCurrentUserId(state);
         const currentTeamId = getCurrentTeamId(state);
+        const thread = getThread(state, threadId);
 
-        if (isThreadOpen(state, threadId) && window.isActive && !isThreadManuallyUnread(state, threadId)) {
+        if (thread && isThreadOpen(state, threadId) && window.isActive && !isThreadManuallyUnread(state, threadId)) {
             // mark thread as read on the server
             dispatch(updateThreadRead(currentUserId, currentTeamId, threadId, Date.now()));
         }