- QUICK_INDEX_MERGE_SELECT deinitializes its rnd_pos() scan when it reaches EOF, but we 
  need to make the deinitialization in QUICK_INDEX_MERGE_SELECT destructor also. This is because
  certain execution strategies can stop scanning without reaching EOF, then then try to do a full
  table scan on this table. Failure to deinitialize caused the full scan to use (already empty) 
  table->sort and produce zero records.

mysql-test/r/index_merge.result:
  BUG#40974: Incorrect query results when using clause evaluated using range check
  - Testcase
mysql-test/t/index_merge.test:
  BUG#40974: Incorrect query results when using clause evaluated using range check
  - Testcase