Fix two A-list corruption cases.

Fix two A-list corruption cases.

When a meta-element indicates the next layer is all-allocated or all-free,
the next layer is allowed to contain garbage.  The allocator must skip an
all-allocated layer.

Similarly when a free recurses through an all-allocated layer the next layer
must be initialized so we can recurse down into it.

Reported-by: Jonathan Lemon <jlemon@cisco.com>