`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.
testArgs.m_settings.command_line_options["inttest2"] = {"81985529216486895"};
    
    testArgs.m_settings.command_line_options["booltest1"] = {""};
    
    testArgs.m_settings.command_line_options["booltest3"] = {"0"};
    testArgs.m_settings.command_line_options["booltest4"] = {"1"};
    
    testArgs.m_settings.command_line_options["pritest1"] = {"a", "b"};
    testArgs.m_settings.ro_config[""]["pritest2"] = {"a", "b"};
    testArgs.m_settings.command_line_options["pritest3"] = {"a"};
    testArgs.m_settings.ro_config[""]["pritest3"] = {"b"};
    testArgs.m_settings.command_line_options["pritest4"] = {"a","b"};
    testArgs.m_settings.ro_config[""]["pritest4"] = {"c","d"};
    BOOST_CHECK_EQUAL(testArgs.GetArg("strtest1", "default"), "string...");
    BOOST_CHECK_EQUAL(testArgs.GetArg("strtest2", "default"), "default");
    BOOST_CHECK_EQUAL(testArgs.GetArg("inttest1", -1), 12345);
    BOOST_CHECK_EQUAL(testArgs.GetArg("inttest2", -1), 81985529216486895LL);
    BOOST_CHECK_EQUAL(testArgs.GetArg("inttest3", -1), -1);
    BOOST_CHECK_EQUAL(testArgs.GetBoolArg("booltest1", false), true);
    BOOST_CHECK_EQUAL(testArgs.GetBoolArg("booltest2", false), false);
    BOOST_CHECK_EQUAL(testArgs.GetBoolArg("booltest3", false), false);
    BOOST_CHECK_EQUAL(testArgs.GetBoolArg("booltest4", false), true);
    BOOST_CHECK_EQUAL(testArgs.GetArg("pritest1", "default"), "b");
    BOOST_CHECK_EQUAL(testArgs.GetArg("pritest2", "default"), "a");
    BOOST_CHECK_EQUAL(testArgs.GetArg("pritest3", "default"), "a");
    BOOST_CHECK_EQUAL(testArgs.GetArg("pritest4", "default"), "b");
}
BOOST_AUTO_TEST_CASE(util_GetChainName)
{
    TestArgsManager test_args;