2 different problems:
- MYSQL_BIN_LOG::write() did not check if mdl_context.acquire_lock() failed
- Sql_cmd_optimize_table::execute() and Sql_cmd_repair_table::execute()
  called write_bin_log(), which could fail if sql_admin() had already
  called my_eof()

Fixed by adding check for aquire_lock() return status and protect
write_bin_log() in the above two functions with set_overwrite_status().