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

{
    SeedInsecureRand(SeedRand::ZEROS);
    for (int mod=2;mod<11;mod++)
    {
        int mask = 1;
        
        int err = 30*10000./mod*sqrt((1./mod*(1-1./mod))/10000.);
        
        while(mask<mod-1)mask=(mask<<1)+1;
        int count = 0;
        
        for (int i = 0; i < 10000; i++) {
            uint32_t rval;
            do{
                rval=InsecureRand32()&mask;
            }while(rval>=(uint32_t)mod);
            count += rval==0;
        }
        BOOST_CHECK(count<=10000/mod+err);
        BOOST_CHECK(count>=10000/mod-err);
    }
}
BOOST_AUTO_TEST_CASE(util_TimingResistantEqual)