executor: fix CI testSerialSuite.TestIndexJoin31494 npe (#32743)
executor: fix CI testSerialSuite.TestIndexJoin31494 npe (#32743)

close pingcap/tidb#32689
pingcap/tidb,ngaut/tidb,ngaut/tidb,c4pt0r/tidb,c4pt0r/tidb,c4pt0r/tidb,kyle-wang/tidb,c4pt0r/tidb,ngaut/tidb,kyle-wang/tidb,pingcap/tidb,c4pt0r/tidb,kyle-wang/tidb,ngaut/tidb,pingcap/tidb,pingcap/tidb,kyle-wang/tidb,kyle-wang/tidb,ngaut/tidb,c4pt0r/tidb,pingcap/tidb,pingcap/tidb,ngaut/tidb,kyle-wang/tidb