HPCC-11544 Roxie restarted after dali disconnected

Race condition on a dali disconnect MAY cause a core.

Signed-off-by: Richard Chapman <rchapman@hpccsystems.com>
Merge pull request #5956 from richardkchapman/roxie-dali-disconnect-core

HPCC-11544 Roxie restarted after dali disconnected

Reviewed-by: Gavin Halliday <ghalliday@hpccsystems.com>