HPCC-10877 More issues in stepped keyed limits

The steplimit regression tests fail on single-part indexes when
allFilesDynamic=false

Signed-off-by: Richard Chapman <rchapman@hpccsystems.com>
Merge pull request #5422 from richardkchapman/steplimit-assert

HPCC-10877 More issues in stepped keyed limits

Reviewed-by: Gavin Halliday <ghalliday@hpccsystems.com>
Community Edition 4.2.2-rc12 Release Candidate 12

Signed-off-by: Richard Chapman <rchapman@hpccsystems.com>
Merge remote-tracking branch 'origin/candidate-4.2.2' into closedown-4.2.x

Conflicts:
	version.cmake

Signed-off-by: Richard Chapman <rchapman@hpccsystems.com>