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

if (!pwallet) return NullUniValue;
    LOCK(pwallet->cs_wallet);
    std::string label = LabelFromValue(request.params[0]);
    
    UniValue ret(UniValue::VOBJ);
    std::set<std::string> addresses;
    for (const std::pair<const CTxDestination, CAddressBookData>& item : pwallet->m_address_book) {
        if (item.second.IsChange()) continue;
        if (item.second.GetLabel() == label) {
            std::string address = EncodeDestination(item.first);
            
            
            
            bool unique = addresses.emplace(address).second;
            CHECK_NONFATAL(unique);
            
            
            
            
            ret.__pushKV(address, AddressBookDataToJSON(item.second, false));
        }
    }
    if (ret.empty()) {
        throw JSONRPCError(RPC_WALLET_INVALID_LABEL_NAME, std::string("No addresses with label " + label));
    }
    return ret;
},
    };
}
static RPCHelpMan listlabels()