tapdb: fix incorrect asset balances with mixed versions

Because of the versions field being in the GROUP BY clause of the query,
we would get two distinct rows returned for the same asset ID if we had
asset UTXOs with different versions.
But because we use the asset ID as the map key of the data structure we
return, only one of those two entries would be returned, causing the
total amount to be incorrect.

We fix this by removing the asset version field from the GROUP BY
clause, resulting in just one row being returned.
The alternative would be to add the version to the map key and show
balances by asset ID and version instead.

tapdb/assets_store.go

@@ -874,7 +874,6 @@ func (a *AssetStore) QueryBalancesByAsset(ctx context.Context,
 			copy(assetID[:], assetBalance.AssetID[:])
 
 			assetIDBalance := AssetBalance{
-				Version:     assetBalance.Version,
 				Balance:     uint64(assetBalance.Balance),
 				Tag:         assetBalance.AssetTag,
 				Type:        asset.Type(assetBalance.AssetType),

tapdb/sqlc/queries/assets.sql

@@ -293,7 +293,7 @@ LEFT JOIN key_group_info_view
     ON assets.genesis_id = key_group_info_view.gen_asset_id
 WHERE spent = FALSE
 GROUP BY assets.genesis_id, genesis_info_view.asset_id,
-         version, genesis_info_view.asset_tag, genesis_info_view.meta_hash,
+         genesis_info_view.asset_tag, genesis_info_view.meta_hash,
          genesis_info_view.asset_type, genesis_info_view.output_index,
          genesis_info_view.prev_out;