`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.
{
    RecursiveMutex cs;
    do {
        LOCK(cs);
        break;
        BOOST_ERROR("break was swallowed!");
    } while(0);
    do {
        TRY_LOCK(cs, lockTest);
        if (lockTest) {
            BOOST_CHECK(true); 
            break;
        }
        BOOST_ERROR("break was swallowed!");
    } while(0);
}
static const unsigned char ParseHex_expected[65] = {
    0x04, 0x67, 0x8a, 0xfd, 0xb0, 0xfe, 0x55, 0x48, 0x27, 0x19, 0x67, 0xf1, 0xa6, 0x71, 0x30, 0xb7,
    0x10, 0x5c, 0xd6, 0xa8, 0x28, 0xe0, 0x39, 0x09, 0xa6, 0x79, 0x62, 0xe0, 0xea, 0x1f, 0x61, 0xde,
    0xb6, 0x49, 0xf6, 0xbc, 0x3f, 0x4c, 0xef, 0x38, 0xc4, 0xf3, 0x55, 0x04, 0xe5, 0x1e, 0xc1, 0x12,
    0xde, 0x5c, 0x38, 0x4d, 0xf7, 0xba, 0x0b, 0x8d, 0x57, 0x8a, 0x4c, 0x70, 0x2b, 0x6b, 0xf1, 0x1d,
    0x5f
};
BOOST_AUTO_TEST_CASE(util_ParseHex)