zdb: Fix asize overflow in verify_livelist_allocs()

Spacemap entry might be too big to fit into a block pointer ashift.
We hit an assertion trying to run `zdb -bvy` on a large pool.  But
it seems the code does not really need size there, since we only
need to search for a range of offsets, so setting it to zero should
just make btree return position just before the first entry.  I
suspect the previous code could actually miss the first entry
due to this if its size was smaller.

Reviewed-by: Brian Behlendorf <[email protected]>
Reviewed-by: Igor Kozhukhov <[email protected]>
Signed-off-by: Alexander Motin <[email protected]>
Closes #17764

cmd/zdb/zdb.c

@@ -385,7 +385,7 @@ verify_livelist_allocs(metaslab_verify_t *mv, uint64_t txg,
 	sublivelist_verify_block_t svb = {{{0}}};
 	DVA_SET_VDEV(&svb.svb_dva, mv->mv_vdid);
 	DVA_SET_OFFSET(&svb.svb_dva, offset);
-	DVA_SET_ASIZE(&svb.svb_dva, size);
+	DVA_SET_ASIZE(&svb.svb_dva, 0);
 	zfs_btree_index_t where;
 	uint64_t end_offset = offset + size;