HPCC-11308 - ensure transaction object files are released on retry

Files transaction looked up in prepartion for manipulation inside
transaction steps were held (linked) and therefore retained a
read lock on those files. If the preparation failed to lock the
files they were release, however if they succeeded, but
subsequent steps failed they were retained whilst the transaction
mechanism sat in it's retry sleep phase.
The net effect would be that other jobs/users might be blocked
from gaining exclusive access to files that had been referenced
inside a transaction.

Signed-off-by: Jake Smith <jake.smith@lexisnexis.com>