This problem might have been introduced in 06270eaac0 but not sure.
The crash could happen due to a use-after-free memory access:
When deleting an entity with skel in postInit(), deletion would be
delayed by 1 frame because that is how entity_delete() works.
During deletion, RenderObject::children were removed and deleted
but SkeletalSprite::bones still had those pointers.
Additionally an object would delete its children in onUpdate() after
safeKill(), and still proceed to run scripts, which would then possibly
access freed memory too.
This fix causes children to not be deleted until we're out of the update()
cycle, and instead delete children together with the root object.