Chain powers are not extracted

[iand]

Describe the bug:

The chain_powers table is empty after running the storage power actor extractor. I didn't see any errors during the backfill which covered 31881 actor states. The power_actor_claims table which is written by the same task does have data in it.

(see https://protocollabs.slack.com/archives/CT2265RFZ/p1604926790480700?thread_ts=1604921495.478300&cid=CT2265RFZ for a tiny amount of context)

Steps to Reproduce:

Visor Version

visor-v0.2.0+72-ge1942a5-dirty (iand/beefy branch)

This commit: 64d05f2

[frrist]

Most recent changes to the code path were made in #172.

Until this is resolved the values can be extracted from actor_states.

[iand]

For comparison,

sentinel-analysis=> select * from visorstats.power_actor_claims order by lower; 
 lower  | upper  | count 
--------+--------+-------
 140000 | 149999 |  4835
 150000 | 159999 |  2849
 160000 | 169674 |  3018
 170000 | 179999 |  2558
 180000 | 189996 |  4886
 190000 | 199997 |  4989
 200000 | 209996 |  5422
 210000 | 210998 |   516
(8 rows)

sentinel-analysis=> select * from visorstats.chain_powers order by lower; 
 lower | upper | count 
-------+-------+-------
     0 |     0 | 29392
(1 row)

Maybe an issue with height? Is it zero?