ensure we break out if walk back page is 0
ensure we break out if walk back page is 0

this prevents an infinite loop as page was converted to a uint32


Former-commit-id: 19d5843e5206d21faba343663b1b207f7a21eb9e
syscoin/syscoin,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin