HPCC-12626 workunit reload could lose uncommitted writes

A thread that had a workunit locked to update it, could have its
changes lost, by another thread forcing an update with reload.
It should have waited until the lock was relinquished.

Signed-off-by: Jake Smith <jake.smith@lexisnexis.com>
Merge pull request #6669 from jakesmith/hpcc-12626

HPCC-12626 workunit reload could lose uncommitted writes

Reviewed-By: Richard Chapman <rchapman@hpccsystems.com>