🐛(frontend) refetch waiting participants when the lobby becomes disabled

When the lobby is disabled mid-meeting (e.g. the room is switched to
public), the waiting participants list stopped being refetched, so
the previously cached list stayed visible with stale data.

Trigger a refetch in that case as well, so the list is cleared and
the moderator UI no longer shows waiting participants for a lobby
that is no longer active.

src/frontend/src/features/rooms/components/LobbyProvider.tsx

@@ -79,7 +79,7 @@ export const LobbyProvider = () => {
   // 3. Rights regained.
   const prevCanManageLobby = usePrevious(canManageLobby)
   useEffect(() => {
-    if (!prevCanManageLobby && canManageLobby && isConnected) {
+    if (prevCanManageLobby != canManageLobby && isConnected) {
       fetchIfManager()
     }
   }, [