fix thread fallback targeting only thread relations (#8006)

Author: Germain

src/components/structures/ThreadView.tsx

@@ -181,7 +181,7 @@ export default class ThreadView extends React.Component<IProps, IState> {
             this.setState({
                 thread,
                 lastThreadReply: thread.lastReply((ev: MatrixEvent) => {
-                    return ev.isThreadRelation && !ev.status;
+                    return ev.isRelation(RelationType.Thread) && !ev.status;
                 }),
             }, async () => {
                 thread.emit(ThreadEvent.ViewThread);
@@ -201,7 +201,7 @@ export default class ThreadView extends React.Component<IProps, IState> {
         if (this.state.thread) {
             this.setState({
                 lastThreadReply: this.state.thread.lastReply((ev: MatrixEvent) => {
-                    return ev.isThreadRelation && !ev.status;
+                    return ev.isRelation(RelationType.Thread) && !ev.status;
                 }),
             });
         }