MM-33359 corrected unread replies update (#17068)

Co-authored-by: Mattermod <mattermod@users.noreply.github.com>

store/sqlstore/thread_store.go

@@ -501,14 +501,22 @@ func (s *SqlThreadStore) DeleteMembershipForUser(userId string, postId string) e
 	return nil
 }
 
-func (s *SqlThreadStore) CreateMembershipIfNeeded(userId, postId string, following, incrementMentions, updateFollowing bool) error {
+func (s *SqlThreadStore) MaintainMembership(userId, postId string, following, incrementMentions, updateFollowing, updateViewedTimestamp bool) error {
 	membership, err := s.GetMembershipForUser(userId, postId)
 	now := utils.MillisFromTime(time.Now())
+	// if memebership exists, update it if:
+	// a. user started/stopped following a thread
+	// b. mention count changed
+	// c. user viewed a thread
 	if err == nil {
-		if (updateFollowing && !membership.Following || membership.Following != following) || incrementMentions {
-			if updateFollowing {
+		followingNeedsUpdate := (updateFollowing && !membership.Following || membership.Following != following)
+		if followingNeedsUpdate || incrementMentions || updateViewedTimestamp {
+			if followingNeedsUpdate {
 				membership.Following = following
 			}
+			if updateViewedTimestamp {
+				membership.LastViewed = now
+			}
 			membership.LastUpdated = now
 			if incrementMentions {
 				membership.UnreadMentions += 1