`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.
{
    int64_t n;
    
    BOOST_CHECK(ParseInt64("1234", nullptr));
    BOOST_CHECK(ParseInt64("0", &n) && n == 0LL);
    BOOST_CHECK(ParseInt64("1234", &n) && n == 1234LL);
    BOOST_CHECK(ParseInt64("01234", &n) && n == 1234LL); 
    BOOST_CHECK(ParseInt64("2147483647", &n) && n == 2147483647LL);
    BOOST_CHECK(ParseInt64("-2147483648", &n) && n == -2147483648LL);
    BOOST_CHECK(ParseInt64("9223372036854775807", &n) && n == (int64_t)9223372036854775807);
    BOOST_CHECK(ParseInt64("-9223372036854775808", &n) && n == (int64_t)-9223372036854775807-1);
    BOOST_CHECK(ParseInt64("-1234", &n) && n == -1234LL);
    
    BOOST_CHECK(!ParseInt64("", &n));
    BOOST_CHECK(!ParseInt64(" 1", &n)); 
    BOOST_CHECK(!ParseInt64("1 ", &n));
    BOOST_CHECK(!ParseInt64("1a", &n));
    BOOST_CHECK(!ParseInt64("aap", &n));
    BOOST_CHECK(!ParseInt64("0x1", &n)); 
    const char test_bytes[] = {'1', 0, '1'};
    std::string teststr(test_bytes, sizeof(test_bytes));
    BOOST_CHECK(!ParseInt64(teststr, &n)); 
    
    BOOST_CHECK(!ParseInt64("-9223372036854775809", nullptr));
    BOOST_CHECK(!ParseInt64("9223372036854775808", nullptr));
    BOOST_CHECK(!ParseInt64("-32482348723847471234", nullptr));
    BOOST_CHECK(!ParseInt64("32482348723847471234", nullptr));
}
BOOST_AUTO_TEST_CASE(test_ParseUInt32)