`FormatMoney(CAmount n)` is not being properly defined for `n = std::numeric_limits<CAmount>::min()`. This is due to an invalid integer negation: the negation of `-9223372036854775808` cannot be represented in type `CAmount` (which has a max value of `9223372036854775807`):

https://github.com/bitcoin/bitcoin/blob/54f812d9d29893c690ae06b84aaeab128186aa36/src/util/moneystr.cpp#L12-L31

FWIW `FormatMoney(-9223372036854775808)` returns `--92233720368.-54775808` when compiled with UBSan (LLVM/Clang, `-fsanitize=undefined`).

Context: https://github.com/bitcoin/bitcoin/pull/20383#discussion_r523250890

It would be nice if `FormatMoney(CAmount n)` was properly defined for all `CAmount n` :)

These are the "expectations of least surprise":

```
BOOST_CHECK_EQUAL(FormatMoney(std::numeric_limits<CAmount>::max()), "92233720368.54775807");       //  9223372036854775807
BOOST_CHECK_EQUAL(FormatMoney(std::numeric_limits<CAmount>::max() - 1), "92233720368.54775806");   //  9223372036854775806
BOOST_CHECK_EQUAL(FormatMoney(std::numeric_limits<CAmount>::max() - 2), "92233720368.54775805");   //  9223372036854775805
BOOST_CHECK_EQUAL(FormatMoney(std::numeric_limits<CAmount>::max() - 3), "92233720368.54775804");   //  9223372036854775804
BOOST_CHECK_EQUAL(FormatMoney(std::numeric_limits<CAmount>::min() + 3), "-92233720368.54775805");  // -9223372036854775805
BOOST_CHECK_EQUAL(FormatMoney(std::numeric_limits<CAmount>::min() + 2), "-92233720368.54775806");  // -9223372036854775806
BOOST_CHECK_EQUAL(FormatMoney(std::numeric_limits<CAmount>::min() + 1), "-92233720368.54775807");  // -9223372036854775807
BOOST_CHECK_EQUAL(FormatMoney(std::numeric_limits<CAmount>::min()), "-92233720368.54775808");      // -9223372036854775808
```

These assertions are _guaranteed_ to hold for all cases above _except_ for the last one.
{
    BOOST_CHECK_THROW(AmountFromValue(ValueFromString("-0.00000001")), UniValue);
    BOOST_CHECK_EQUAL(AmountFromValue(ValueFromString("0")), 0LL);
    BOOST_CHECK_EQUAL(AmountFromValue(ValueFromString("0.00000000")), 0LL);
    BOOST_CHECK_EQUAL(AmountFromValue(ValueFromString("0.00000001")), 1LL);
    BOOST_CHECK_EQUAL(AmountFromValue(ValueFromString("0.17622195")), 17622195LL);
    BOOST_CHECK_EQUAL(AmountFromValue(ValueFromString("0.5")), 50000000LL);
    BOOST_CHECK_EQUAL(AmountFromValue(ValueFromString("0.50000000")), 50000000LL);
    BOOST_CHECK_EQUAL(AmountFromValue(ValueFromString("0.89898989")), 89898989LL);
    BOOST_CHECK_EQUAL(AmountFromValue(ValueFromString("1.00000000")), 100000000LL);
    BOOST_CHECK_EQUAL(AmountFromValue(ValueFromString("20999999.9999999")), 2099999999999990LL);
    BOOST_CHECK_EQUAL(AmountFromValue(ValueFromString("20999999.99999999")), 2099999999999999LL);
    BOOST_CHECK_EQUAL(AmountFromValue(ValueFromString("1e-8")), COIN/100000000);
    BOOST_CHECK_EQUAL(AmountFromValue(ValueFromString("0.1e-7")), COIN/100000000);
    BOOST_CHECK_EQUAL(AmountFromValue(ValueFromString("0.01e-6")), COIN/100000000);
    BOOST_CHECK_EQUAL(AmountFromValue(ValueFromString("0.0000000000000000000000000000000000000000000000000000000000000000000000000001e+68")), COIN/100000000);
    BOOST_CHECK_EQUAL(AmountFromValue(ValueFromString("10000000000000000000000000000000000000000000000000000000000000000e-64")), COIN);
    BOOST_CHECK_EQUAL(AmountFromValue(ValueFromString("0.000000000000000000000000000000000000000000000000000000000000000100000000000000000000000000000000000000000000000000000e64")), COIN);
    BOOST_CHECK_THROW(AmountFromValue(ValueFromString("1e-9")), UniValue); 
    BOOST_CHECK_THROW(AmountFromValue(ValueFromString("0.000000019")), UniValue); 
    BOOST_CHECK_EQUAL(AmountFromValue(ValueFromString("0.00000001000000")), 1LL); 
    BOOST_CHECK_THROW(AmountFromValue(ValueFromString("19e-9")), UniValue); 
    BOOST_CHECK_EQUAL(AmountFromValue(ValueFromString("0.19e-6")), 19); 
    BOOST_CHECK_THROW(AmountFromValue(ValueFromString("92233720368.54775808")), UniValue); 
    BOOST_CHECK_THROW(AmountFromValue(ValueFromString("1e+11")), UniValue); 
    BOOST_CHECK_THROW(AmountFromValue(ValueFromString("1e11")), UniValue); 
    BOOST_CHECK_THROW(AmountFromValue(ValueFromString("93e+9")), UniValue); 
}
BOOST_AUTO_TEST_CASE(json_parse_errors)