This is needed to avoid running into out of buffer situations
where we cannot alloc a new buffer because we hit the array size
limit (ZBUF).
Use a combined allocation for the struct and the actual data buffer
to not increase the number of malloc calls. [1]
Defer initialization of zbuf until we actually need it.
Make sure the output buffer will be large enough in all cases.
Details discussed with: kib [1]
Reviewed by: kib [1]
MFC after: 6 days
3fae6ec1cf