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

#include <policy/rbf.h>
#include <rpc/rawtransaction_util.h>
#include <rpc/server.h>
#include <rpc/util.h>
#include <script/descriptor.h>
#include <script/sign.h>
#include <util/bip32.h>
#include <util/fees.h>
#include <util/message.h> 
#include <util/moneystr.h>
#include <util/string.h>
#include <util/system.h>
#include <util/translation.h>
#include <util/url.h>
#include <util/vector.h>
#include <wallet/coincontrol.h>
#include <wallet/context.h>
#include <wallet/feebumper.h>
#include <wallet/load.h>
#include <wallet/rpcwallet.h>
#include <wallet/wallet.h>
#include <wallet/walletdb.h>
#include <wallet/walletutil.h>
#include <optional>
#include <stdint.h>
#include <univalue.h>
using interfaces::FoundBlock;
static const std::string WALLET_ENDPOINT_BASE = "/wallet/";
static const std::string HELP_REQUIRING_PASSPHRASE{"\nRequires wallet passphrase to be set with walletpassphrase call if wallet is encrypted.\n"};
static inline bool GetAvoidReuseFlag(const CWallet& wallet, const UniValue& param) {