[#45] nns: Fix inconsistent fee of register operations

Signed-off-by: Alex Vanin <a.vanin@yadro.com>

nns/nns_contract.go

@@ -458,13 +458,13 @@ func updateBalance(ctx storage.Context, tokenId []byte, acc interop.Hash160, dif
 	balanceKey := append([]byte{prefixBalance}, acc...)
 	var balance int
 	if b := storage.Get(ctx, balanceKey); b != nil {
-		balance = b.(int)
+		balance = common.FromFixedWidth64(b.([]byte))
 	}
 	balance += diff
 	if balance == 0 {
 		storage.Delete(ctx, balanceKey)
 	} else {
-		storage.Put(ctx, balanceKey, balance)
+		storage.Put(ctx, balanceKey, common.ToFixedWidth64(balance))
 	}
 
 	tokenKey := getTokenKey(tokenId)
@@ -488,14 +488,14 @@ func postTransfer(from, to interop.Hash160, tokenID []byte, data interface{}) {
 // getTotalSupply returns total supply from storage.
 func getTotalSupply(ctx storage.Context) int {
 	val := storage.Get(ctx, []byte{prefixTotalSupply})
-	return val.(int)
+	return common.FromFixedWidth64(val.([]byte))
 }
 
 // updateTotalSupply adds the specified diff to the total supply.
 func updateTotalSupply(ctx storage.Context, diff int) {
 	tsKey := []byte{prefixTotalSupply}
 	ts := getTotalSupply(ctx)
-	storage.Put(ctx, tsKey, ts+diff)
+	storage.Put(ctx, tsKey, common.ToFixedWidth64(ts+diff))
 }
 
 // getTokenKey computes hash160 from the given tokenID.