Per-row bulk execution is not reprepared on Galera

Found by code review, not reproduced (no Galera setup).

In Prepared_statement::execute_bulk_loop() the reprepare is in the else branch of the WSREP check:

#ifdef WITH_WSREP

    if (!bulk_optimized && WSREP(thd))      // !CF_PS_ARRAY_BINDING_OPTIMIZED before MDEV-23864

    {

      if (wsrep_after_statement(thd))

      { ... }

    }

    else

#endif /* WITH_WSREP */

    if (unlikely(error) &&

        (sql_command_flags[lex->sql_command] & CF_REEXECUTION_FRAGILE) &&

        ... reprepare_observer.is_invalidated() ...)

    {

      thd->clear_error();

      error= reprepare();

      ...

So on a Galera node a bulk UPDATE/DELETE (and, after MDEV-23864, INSERT/REPLACE with a subquery depending on a parameter) whose tables changed after PREPARE should return ER_NEED_REPREPARE to the client instead of being reprepared. Prepared_statement::execute_loop() reprepares in this case.