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

{
    std::vector<std::string> comments;
    comments.push_back(std::string("comment1"));
    std::vector<std::string> comments2;
    comments2.push_back(std::string("comment1"));
    comments2.push_back(SanitizeString(std::string("Comment2; .,_?@-; !\"#$%&'()*+/<=>[]\\^`{|}~"), SAFE_CHARS_UA_COMMENT)); 
    BOOST_CHECK_EQUAL(FormatSubVersion("Test", 99900, std::vector<std::string>()),std::string("/Test:9.99.0/"));
    BOOST_CHECK_EQUAL(FormatSubVersion("Test", 99900, comments),std::string("/Test:9.99.0(comment1)/"));
    BOOST_CHECK_EQUAL(FormatSubVersion("Test", 99900, comments2),std::string("/Test:9.99.0(comment1; Comment2; .,_?@-; )/"));
}
BOOST_AUTO_TEST_CASE(test_ParseFixedPoint)
{
    int64_t amount = 0;
    BOOST_CHECK(ParseFixedPoint("0", 8, &amount));
    BOOST_CHECK_EQUAL(amount, 0LL);
    BOOST_CHECK(ParseFixedPoint("1", 8, &amount));
    BOOST_CHECK_EQUAL(amount, 100000000LL);
    BOOST_CHECK(ParseFixedPoint("0.0", 8, &amount));
    BOOST_CHECK_EQUAL(amount, 0LL);
    BOOST_CHECK(ParseFixedPoint("-0.1", 8, &amount));
    BOOST_CHECK_EQUAL(amount, -10000000LL);
    BOOST_CHECK(ParseFixedPoint("1.1", 8, &amount));