If compression happend, any garbage past the compress size was not
zeroed out.
If compression didn't happen, then the payload size was still set to
the rounded-up return from zio_compress_data(), which is dependent on
the input, which is not necessarily the logical size.
So that's all fixed too, mostly from stealing the math from zio.c.
Sponsored-by: Klara, Inc.
Sponsored-by: Wasabi Technology, Inc.
Signed-off-by: Rob Norris <rob.norris@klarasystems.com>
cb36f4f352