values smaller than 0.001 sat/B can't be represented by CFeeRate, but they are not rejected.

```
./src/bitcoin-cli -named sendtoaddress address=bcrt1qwkmhqum095zau5rf2velq55cq938vrd7uw8m4r amount=1.23 fee_rate=0.0009

error code: -6
error message:
Fee rate (0.000 sat/vB) is lower than the minimum fee rate setting (1.000 sat/vB)
```

```
./src/bitcoin-cli -named sendtoaddress address=bcrt1qwkmhqum095zau5rf2velq55cq938vrd7uw8m4r amount=1.23 fee_rate=0.000000000009

error code: -3
error message:
Invalid amount

throw JSONRPCError(RPC_INVALID_ADDRESS_OR_KEY, std::string("Invalid Bitcoin address: ") + input.get_str());
            }
            if (!destinations.insert(dest).second) {
                throw JSONRPCError(RPC_INVALID_PARAMETER, std::string("Invalid parameter, duplicated address: ") + input.get_str());
            }
        }
    }
    bool include_unsafe = true;
    if (!request.params[3].isNull()) {
        RPCTypeCheckArgument(request.params[3], UniValue::VBOOL);
        include_unsafe = request.params[3].get_bool();
    }
    CAmount nMinimumAmount = 0;
    CAmount nMaximumAmount = MAX_MONEY;
    CAmount nMinimumSumAmount = MAX_MONEY;
    uint64_t nMaximumCount = 0;
    if (!request.params[4].isNull()) {
        const UniValue& options = request.params[4].get_obj();
        RPCTypeCheckObj(options,
            {
                {"minimumAmount", UniValueType()},
                {"maximumAmount", UniValueType()},
                {"minimumSumAmount", UniValueType()},
                {"maximumCount", UniValueType(UniValue::VNUM)},
            },
            true, true);
        if (options.exists("minimumAmount"))
            nMinimumAmount = AmountFromValue(options["minimumAmount"]);
        if (options.exists("maximumAmount"))
            nMaximumAmount = AmountFromValue(options["maximumAmount"]);