wallet: Use chain.lock() instead of temporary chain.assumeLocked()
wallet: Use chain.lock() instead of temporary chain.assumeLocked()

Former-commit-id: 6642c48895c1424d9fd5824669b80532d0586ec4
syscoin/syscoin,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin