HPCC-9350 - Fix DISTRIBUTE,SKEW assert

gh-4332 introduced a regression, where by DISTRIBUTE,SKEW would
assert during destruction.

Signed-off-by: Jake Smith <jake.smith@lexisnexis.com>
Merge pull request #4389 from jakesmith/redist-bug

HPCC-9350 - Fix DISTRIBUTE,SKEW assert

Reviewed-By: Gavin Halliday <gavin.halliday@lexisnexis.com>
Reviewed-By: Richard Chapman <rchapman@hpccsystems.com>