The basic storage has an implicit invariant that if the size of the
storage is 0 then the array is a null pointer. That invariant was broken
if the array was allocated and then Shrink or Allocate was called with
0. In that case, the array remained allocated by the size was set to 0.

This fixes the problem by making sure a Shrink(0) actually does an
Allocate(0) (to clear out the data) and that the basic storage always
frees its memory when allocating a 0 sized array.