HPCC-10048 Fix uninitialised variable in XREFDirectoryBuilder::getDirectory

If it had an exception attempting to read the directory it could have
continually retried, waiting for an unpredictable time between retries.

Signed-off-by: Gavin Halliday <gavin.halliday@lexisnexis.com>
Merge pull request #4846 from ghalliday/issue10048

HPCC-10048 Fix uninitialised variable in XREFDirectoryBuilder::getDirectory

Reviewed-By: Richard Chapman <rchapman@hpccsystems.com>