`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(test_args.GetArgs("-a").size() == 1
                && test_args.GetArgs("-a").front() == "");
    BOOST_CHECK(test_args.GetArgs("-b").size() == 1
                && test_args.GetArgs("-b").front() == "1");
    BOOST_CHECK(test_args.GetArgs("-ccc").size() == 2
                && test_args.GetArgs("-ccc").front() == "argument"
                && test_args.GetArgs("-ccc").back() == "multiple");
    BOOST_CHECK(test_args.GetArgs("-fff").size() == 0);
    BOOST_CHECK(test_args.GetArgs("-nofff").size() == 0);
    BOOST_CHECK(test_args.GetArgs("-ggg").size() == 1
                && test_args.GetArgs("-ggg").front() == "1");
    BOOST_CHECK(test_args.GetArgs("-noggg").size() == 0);
    BOOST_CHECK(test_args.GetArgs("-h").size() == 0);
    BOOST_CHECK(test_args.GetArgs("-noh").size() == 0);
    BOOST_CHECK(test_args.GetArgs("-i").size() == 1
                && test_args.GetArgs("-i").front() == "1");
    BOOST_CHECK(test_args.GetArgs("-noi").size() == 0);
    BOOST_CHECK(test_args.GetArgs("-zzz").size() == 0);
    BOOST_CHECK(!test_args.IsArgNegated("-a"));
    BOOST_CHECK(!test_args.IsArgNegated("-b"));
    BOOST_CHECK(!test_args.IsArgNegated("-ccc"));
    BOOST_CHECK(!test_args.IsArgNegated("-d"));
    BOOST_CHECK(test_args.IsArgNegated("-fff"));
    BOOST_CHECK(!test_args.IsArgNegated("-ggg"));
    BOOST_CHECK(test_args.IsArgNegated("-h")); 
    BOOST_CHECK(!test_args.IsArgNegated("-i")); 
    BOOST_CHECK(!test_args.IsArgNegated("-zzz"));
    
    test_args.SelectConfigNetwork("sec1");