wallet_balance.py: Prevent edge cases
wallet_balance.py: Prevent edge cases


Former-commit-id: d2f30ba3f8b928e9fd002b58c1a0b48fb27759d2
syscoin/syscoin,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin