reset errors (in thd) before executing the event. Otherwise if an event is ignored
because of replicate-*-table rules (error ER_SLAVE_IGNORED_TABLE) this error code
may remain in thd->net and the next event may pick it. 


sql/log_event.cc:
  Reset errors (in thd) before executing the event. Otherwise if an event is ignored
  because of replicate-*-table rules (error ER_SLAVE_IGNORED_TABLE) this error code
  may remain in thd->net and the next event may pick it.