Checkmk Werk 13867: Fix update preview of bulk import of hosts

ID: 13867 Title: Fix update preview of bulk import of hosts Component: Multisite Level: 1 Class: Bug fix Version: 2.2.0i1 Werk #13675 fixed a NoneType error on updating the preview but the header was not rendered correctly after that fix. The header is now rendered as intended with and without the option "Has title line".