tapdb: wrap error in QueryAssets

This was found in the unit test that will be added in the next commit.
We need to wrap database errors in order for us to parse them correctly
as database specific typed errors.

Author: guggero

tapdb/assets_store.go

@@ -861,7 +861,7 @@ func fetchAssetsWithWitness(ctx context.Context, q ActiveAssetsStore,
 	// First, we'll fetch all the assets we know of on disk.
 	dbAssets, err := q.QueryAssets(ctx, assetFilter)
 	if err != nil {
-		return nil, nil, fmt.Errorf("unable to read db assets: %v", err)
+		return nil, nil, fmt.Errorf("unable to read db assets: %w", err)
 	}
 
 	assetIDs := fMap(dbAssets, func(a ConfirmedAsset) int64 {