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

"1KqbBpLy5FARmTPD4VZnDDpYjkUvkr82Pm",
            "invalid signature, not in base64 encoding",
            "message should be irrelevant"),
        MessageVerificationResult::ERR_MALFORMED_SIGNATURE);
    BOOST_CHECK_EQUAL(
        MessageVerify(
            "1KqbBpLy5FARmTPD4VZnDDpYjkUvkr82Pm",
            "AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA=",
            "message should be irrelevant"),
        MessageVerificationResult::ERR_PUBKEY_NOT_RECOVERED);
    BOOST_CHECK_EQUAL(
        MessageVerify(
            "15CRxFdyRpGZLW9w8HnHvVduizdL5jKNbs",
            "IPojfrX2dfPnH26UegfbGQQLrdK844DlHq5157/P6h57WyuS/Qsl+h/WSVGDF4MUi4rWSswW38oimDYfNNUBUOk=",
            "I never signed this"),
        MessageVerificationResult::ERR_NOT_SIGNED);
    BOOST_CHECK_EQUAL(
        MessageVerify(
            "15CRxFdyRpGZLW9w8HnHvVduizdL5jKNbs",
            "IPojfrX2dfPnH26UegfbGQQLrdK844DlHq5157/P6h57WyuS/Qsl+h/WSVGDF4MUi4rWSswW38oimDYfNNUBUOk=",
            "Trust no one"),
        MessageVerificationResult::OK);
    BOOST_CHECK_EQUAL(
        MessageVerify(
            "11canuhp9X2NocwCq7xNrQYTmUgZAnLK3",
            "IIcaIENoYW5jZWxsb3Igb24gYnJpbmsgb2Ygc2Vjb25kIGJhaWxvdXQgZm9yIGJhbmtzIAaHRtbCeDZINyavx14=",
            "Trust me"),
        MessageVerificationResult::OK);
}
BOOST_AUTO_TEST_CASE(message_hash)