fix typing

Author: rodja

nicegui/storage.py

@@ -165,8 +165,9 @@ async def _create_tab_storage(self, tab_id: str) -> None:
         if tab_id not in self._tabs:
             if Storage.redis_url:
                 self._tabs[tab_id] = Storage._create_persistent_dict(f'tab-{tab_id}')
-                assert isinstance(self._tabs[tab_id], PersistentDict)
-                await self._tabs[tab_id].initialize()
+                tab = self._tabs[tab_id]
+                if isinstance(tab, PersistentDict):
+                    await tab.initialize()
             else:
                 self._tabs[tab_id] = ObservableDict()