Add some diagnostic code to track BLOB bugs if they were not already fixed with the change in row0sel.c
row0sel.c:
  Fix a seg fault which was caused inside MySQL because InnoDB when returning a BLOB value did not initialize the length and the data pointer of a BLOB whose value is the SQL NULL; also fix a very improbable race condition which could occur if a row with an externally stored BLOB was fetched using the adaptive hash index