HPCC-12767 Regression in splitter, could cause divide by zero.

Changes in HPCC-12633 meant a divide by zero, if the input had an
unknown min record size (0).

Code generator should generate a min size of 1, when known, see
issue HPCC-12768

Signed-off-by: Jake Smith <jake.smith@lexisnexis.com>
Merge pull request #6779 from jakesmith/hpcc-12767

HPCC-12767 Regression in splitter, could cause divide by zero.

Reviewed-by: Gavin Halliday <ghalliday@hpccsystems.com>