Don't try to sync NFT prices

[bohendo]

While generating a list of missing prices, skip any without an amount. Requires resolution of #158

[bohendo]

Also, why are so many NFT prices missing? They should have been calculated. Ensure we're we only trying to sync currently held NFT prices.

Also, why are we trying to sync 2 missing NFT prices? If we're only syncing currently held ones, that should be just 1 missing price..