explicitly fallback to None for invalid/empty room topics

Signed-off-by: strawberry <strawberry@puppygock.gay>

src/api/client_server/directory.rs

@@ -247,7 +247,7 @@ pub(crate) async fn get_public_rooms_filtered_helper(
                                 Error::bad_database("Invalid room topic event in database.")
                             })
                     })
-                    .unwrap_or_default(),
+                    .unwrap_or(None),
                 world_readable: services()
                     .rooms
                     .state_accessor

src/service/rooms/spaces/mod.rs

@@ -347,7 +347,7 @@ impl Service {
                             Error::bad_database("Invalid room topic event in database.")
                         })
                 })
-                .unwrap_or_default(),
+                .unwrap_or(None),
             world_readable: services()
                 .rooms
                 .state_accessor