HPCC-9279 REGRESSION - ESP cored when trying to view a file

Changes for issue HPCC-9178 introduced a core on systems with no
authentication set up.

Signed-off-by: Richard Chapman <rchapman@hpccsystems.com>
Merge pull request #4358 from richardkchapman/esp-core

HPCC-9279 REGRESSION - ESP cored when trying to view a file

Reviewed-by: Gavin Halliday <ghalliday@hpccsystems.com>