test: add two edge case tests for CSubNet
test: add two edge case tests for CSubNet

Former-commit-id: 3e9235193ec2e99873506d35459cc39974cdd22b
syscoin/syscoin,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin