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

Tracker(const Tracker& t) noexcept : origin(t.origin), copies(t.copies + 1) {}
    Tracker(Tracker&& t) noexcept : origin(t.origin), copies(t.copies) {}
    Tracker& operator=(const Tracker& t) noexcept
    {
        origin = t.origin;
        copies = t.copies + 1;
        return *this;
    }
};
}
BOOST_AUTO_TEST_CASE(test_tracked_vector)
{
    Tracker t1;
    Tracker t2;
    Tracker t3;
    BOOST_CHECK(t1.origin == &t1);
    BOOST_CHECK(t2.origin == &t2);
    BOOST_CHECK(t3.origin == &t3);