HPCC-8960 Uninitialized variable in dadfs (rename physical)

Introduced during 4.0 closedown.

Signed-off-by: Richard Chapman <rchapman@hpccsystems.com>
Merge pull request #4094 from richardkchapman/uninit-dafs

HPCC-8960 Uninitialized variable in dadfs (rename physical)

Reviewed-by: Gavin Halliday <ghalliday@hpccsystems.com>