Nested Multicol Two Spanners Dynamic

PASS if no crash.

1. After initial layout: A multicol has a column-span:all descendant (not a direct child, so that we establish block continuations and anonymous multi-column blocks)
2. Turn a child of this multicol container into a multicol
3. Add another column-span:all descendant (again, not a direct child, so that we get more continuations)
4. Set display:none on everything