HPCC-8545 Open Workunit not work for archived WU in ECLWatch

Access check is added recently when a user trys to retrieve ECL WU
information. The access check has to open the workunit. An exception
is thrown when failed to open workunit for archived WU. This fix
detects the exception and calls GetArchivedWUInfo() to retrieve the
WU info.

Signed-off-by: Kevin Wang <kevin.wang@lexisnexis.com>