The continue statement in bch2_trans_mark_extent() was wrong - by
bailing out early, we'd be constructing the wrong replicas list to
update. Also, the assertion in update_replicas() was wrong - due to
rounding with compressed extents, it is possible for sectors to be 0
sometimes.

Also, change extent_to_replicas() in replicas.c to match the replicas
list we construct in buckets.c.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>