don't try to build secondary indexes if we don't need them (#17246)

runtime/src/accounts_db.rs

@@ -5054,6 +5054,7 @@ impl AccountsDb {
                             }
                         }
                         drop(lock);
+                        if !self.account_indexes.is_empty() {
                             for (pubkey, account_infos) in accounts_map.into_iter() {
                                 for (_, (_store_id, stored_account)) in account_infos.iter() {
                                     self.accounts_index.update_secondary_indexes(
@@ -5066,6 +5067,7 @@ impl AccountsDb {
                             }
                         }
                     }
+                }
                 scan_time_sum
             })
             .sum();