zbd: engines/libzbc: don't fail on assert for offline zones

zbd: engines/libzbc: don't fail on assert for offline zones

If fio is run against a zoned device that has any zones in OFFLINE
condition, the following assertion is raised -

fio: zbd.c:473: parse_zone_info: Assertion `z->wp <= z->start + zone_size' failed.

This happens because offline zones have no valid write pointer and
it is reported by libzbc and blkzoned as (uint64_t)(-1). To avoid
violating this assertion, set the write pointer in all offline zones
to point at the start of the zone.

Signed-off-by: Dmitry Fomichev <dmitry.fomichev@wdc.com>
Reviewed-by: Shin'ichiro Kawasaki <shinichiro.kawasaki@wdc.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>