MDEV-7906: InnoDB: Failing assertion: prebuilt->sql_stat_start || trx->state == 1 on concurrent multi-table update

Analysis: Problem is that SQL-layer calls handler API after storage
engine has already returned error state. InnoDB does internal
rollback when it notices transaction error (e.g. lock wait timeout,
deadlock, etc.) and after this transaction is not naturally in
correct state to continue.

Fix: Do not continue fetch operations if transaction is not started.