- In join buffering code, call join_tab_execution_startup() (#1) before we call join_tab_scan->open() (#2).
  This is important with SJ-Materialization because #1 fills the materialized table, while
  #2 will actually try to read the first row. Attempt to read the first row before we have
  populated the materialized table would cause zero rows to be returned when actually there were matches.