Broken validation in block attributes.

Steps:

1. Edit Dashboard page / Landing page.
2. Add Recent activity (or Ibexa news) / Content List block.
3. Open block settings.
4. In Limit field enter e.g. negative number.
5. Save changes.

Actual result: Validation from configuration is not applied. Block preview disappears.
Expected result: Validation applied.

Remarks: Does not affect 4.5.