core/storage: Allocate page1 lazily for MVCC transactions

core/vdbe/execute.rs

@@ -1944,6 +1944,8 @@ pub fn op_transaction(
 
     if let Some(mv_store) = &mv_store {
         if state.mv_tx_id.is_none() {
+            // We allocate the first page lazily in the first transaction.
+            return_if_io!(pager.maybe_allocate_page1());
             let tx_id = mv_store.begin_tx();
             conn.mv_transactions.borrow_mut().push(tx_id);
             state.mv_tx_id = Some(tx_id);