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 (!value.isNum() && !value.isStr())
        throw JSONRPCError(RPC_TYPE_ERROR, "Amount is not a number or string");
    CAmount amount;
    if (!ParseFixedPoint(value.getValStr(), 8, &amount))
        throw JSONRPCError(RPC_TYPE_ERROR, "Invalid amount");
    if (!MoneyRange(amount))
        throw JSONRPCError(RPC_TYPE_ERROR, "Amount out of range");
    return amount;
}
uint256 ParseHashV(const UniValue& v, std::string strName)
{
    std::string strHex(v.get_str());
    if (64 != strHex.length())
        throw JSONRPCError(RPC_INVALID_PARAMETER, strprintf("%s must be of length %d (not %d, for '%s')", strName, 64, strHex.length(), strHex));
    if (!IsHex(strHex)) 
        throw JSONRPCError(RPC_INVALID_PARAMETER, strName+" must be hexadecimal string (not '"+strHex+"')");
    return uint256S(strHex);
}
uint256 ParseHashO(const UniValue& o, std::string strKey)