HPCC-10686 - Need to check subfile after lock retry

Need to check if subfile provided in RemoveSubFile when
rechcking if sub is member of super after dirty lock.
subfile is empty in case of ClearSuperFile(calling RemoveSubFile)

Signed-off-by: Jake Smith <jake.smith@lexisnexis.com>
Merge pull request #5296 from jakesmith/hpcc-10686

HPCC-10686 - Need to check subfile after lock retry

Reviewed-By: Richard Chapman <rchapman@hpccsystems.com>