`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_EQUAL(Join({}, ", "), "");
    BOOST_CHECK_EQUAL(Join({"foo"}, ", "), "foo");
    BOOST_CHECK_EQUAL(Join({"foo", "bar"}, ", "), "foo, bar");
    
    const auto op_upper = [](const std::string& s) { return ToUpper(s); };
    BOOST_CHECK_EQUAL(Join<std::string>({}, ", ", op_upper), "");
    BOOST_CHECK_EQUAL(Join<std::string>({"foo"}, ", ", op_upper), "FOO");
    BOOST_CHECK_EQUAL(Join<std::string>({"foo", "bar"}, ", ", op_upper), "FOO, BAR");
}
BOOST_AUTO_TEST_CASE(util_FormatParseISO8601DateTime)
{
    BOOST_CHECK_EQUAL(FormatISO8601DateTime(1317425777), "2011-09-30T23:36:17Z");
    BOOST_CHECK_EQUAL(FormatISO8601DateTime(0), "1970-01-01T00:00:00Z");
    BOOST_CHECK_EQUAL(ParseISO8601DateTime("1970-01-01T00:00:00Z"), 0);
    BOOST_CHECK_EQUAL(ParseISO8601DateTime("1960-01-01T00:00:00Z"), 0);
    BOOST_CHECK_EQUAL(ParseISO8601DateTime("2011-09-30T23:36:17Z"), 1317425777);
    auto time = GetSystemTimeInSeconds();
    BOOST_CHECK_EQUAL(ParseISO8601DateTime(FormatISO8601DateTime(time)), time);
}
BOOST_AUTO_TEST_CASE(util_FormatISO8601Date)
{
    BOOST_CHECK_EQUAL(FormatISO8601Date(1317425777), "2011-09-30");
}
struct TestArgsManager : public ArgsManager
{
    TestArgsManager() { m_network_only_args.clear(); }