Jumping out of man_unscope() for the root node is a bad idea

Jumping out of man_unscope() for the root node is a bad idea
because that will skip root node validation, potentially entering
rendering modules will NULL pointers lurking in the meta data.
Instead, always validate the root node and (as suggested by joerg@)
assert validity of the meta data before using it in the renderers.
ok joerg@