HPCC-8728 lack of info. spraying large file(s) whilst partitioning

Insert progress indicator logging into findSplitPoint() function.

Signed-off-by: Attila Vamos <attila.vamos@gmail.com>
Merge pull request #4457 from AttilaVamos/HPCC-8728-improvement

HPCC-8728 lack of info. spraying large file(s) whilst partitioning

Reviewed-By: Richard Chapman <rchapman@hpccsystems.com>