fix(new room list): fix outdated message preview when space change

Author: florianduros

src/components/viewmodels/roomlist/RoomListItemViewModel.tsx

@@ -221,6 +221,7 @@ function useRoomMessagePreview(room: Room): string | undefined {
             roomIsDM ? DefaultTagID.DM : DefaultTagID.Untagged,
         );
         if (messagePreview) setPreviewText(messagePreview.text);
+        else setPreviewText(undefined);
     }, [room, shouldShowMessagePreview]);
 
     // MessagePreviewStore and the other AsyncStores need to be converted to TypedEventEmitter