fix availablecoins
fix availablecoins

was skipping over 0 value coins, not useful for asset updates


Former-commit-id: 56761c3cc0974521682b37ba8c64d61328f9bf52
syscoin/syscoin,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin