`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.
const std::vector<std::string> sec2_ccc_expected = {"extend3","argument","multiple"};
    const auto& sec2_ccc_res = test_args.GetArgs("-ccc");
    BOOST_CHECK_EQUAL_COLLECTIONS(sec2_ccc_res.begin(), sec2_ccc_res.end(), sec2_ccc_expected.begin(), sec2_ccc_expected.end());
    
    test_args.SetNetworkOnlyArg("-d");
    test_args.SetNetworkOnlyArg("-ccc");
    test_args.SetNetworkOnlyArg("-h");
    test_args.SelectConfigNetwork(CBaseChainParams::MAIN);
    BOOST_CHECK(test_args.GetArg("-d", "xxx") == "e");
    BOOST_CHECK(test_args.GetArgs("-ccc").size() == 2);
    BOOST_CHECK(test_args.GetArg("-h", "xxx") == "0");
    test_args.SelectConfigNetwork("sec1");
    BOOST_CHECK(test_args.GetArg("-d", "xxx") == "eee");
    BOOST_CHECK(test_args.GetArgs("-d").size() == 1);
    BOOST_CHECK(test_args.GetArgs("-ccc").size() == 2);
    BOOST_CHECK(test_args.GetArg("-h", "xxx") == "1");
    test_args.SelectConfigNetwork("sec2");
    BOOST_CHECK(test_args.GetArg("-d", "xxx") == "xxx");
    BOOST_CHECK(test_args.GetArgs("-d").size() == 0);
    BOOST_CHECK(test_args.GetArgs("-ccc").size() == 1);
    BOOST_CHECK(test_args.GetArg("-h", "xxx") == "0");
}
BOOST_AUTO_TEST_CASE(util_GetArg)
{
    TestArgsManager testArgs;
    LOCK(testArgs.cs_args);
    testArgs.m_settings.command_line_options.clear();
    testArgs.m_settings.command_line_options["strtest1"] = {"string..."};
    
    testArgs.m_settings.command_line_options["inttest1"] = {"12345"};