the thread->mysys_var parameter should be empty for the idle
    embedded-server threads so that working threads can safely free
    this memory.

per-file comments:
  libmysqld/lib_sql.cc
Bug#43733      Select on processlist let the embedded server crash (concurrent_innodb_safelog)
    set thread->mysys_var= 0 after the query is handled

  mysql-test/include/concurrent.inc
Bug#43733      Select on processlist let the embedded server crash (concurrent_innodb_safelog)
    enable these for the embedded-server mode

  sql/sql_show.cc
Bug#43733      Select on processlist let the embedded server crash (concurrent_innodb_safelog)
    show thread lock status in the query result