As Davi added code like
          sav_protocol= thd->protocol
          thd->protocol= &thd->protocol_binary
          ...
          thd->protocol= sav_protocol
  the fucntions like emb_store_querycache_result() cannot determine
  the used protocol testing thd->protocol == &thd->protocol_binary.
  Fixed by additional check thd->command == COM_STMT_EXECUTE.