message: rpcwallet: Replace boost::optional<T>::emplace with simple assignment of T{}
  Optional::emplace() was only added in boost 1.56, see
  To simply work around
  replace it with assignment of T{}
diff: @@ -1542,8 +1542,8 @@ static UniValue listsinceblock(const JSONRPCRequest& request)
  uint256 blockId;
  if (!request.params[0].isNull() && !request.params[0].get_str().empty()) {
  blockId = ParseHashV(request.params[0], "blockhash");
  - height.emplace();
  - altheight.emplace();
  + height = int{};
  + altheight = int{};
  if (!pwallet->chain().findCommonAncestor(blockId, pwallet->GetLastBlockHash(), /* ancestor out */ FoundBlock().height(*height), /* blockId out */ FoundBlock().height(*altheight))) {
  throw JSONRPCError(RPC_INVALID_ADDRESS_OR_KEY, "Block not found");
  }
  