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

Former-commit-id: 21667f0abfb07480f73d2a6ee6cb235de5e5e12d
syscoin/syscoin,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin