HPCC-8596 Problems dealing with CSV headers in mixed width supers

When have read all local parts, need to check unsent part header
counts from previous node.

Signed-off-by: Jake Smith <jake.smith@lexisnexis.com>
Merge pull request #3850 from jakesmith/supercsv-header

HPCC-8596 Problems dealing with CSV headers in mixed width supers

Reviewed-By: Richard Chapman <rchapman@hpccsystems.com>