`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_NO_THROW(CallRPC("createrawtransaction [{\"txid\":\"a3b807410df0b60fcb9736768df5823938b2f838694939ba45f3c0a1bff150ed\",\"vout\":0}] {\"data\":\"68656c6c6f776f726c64\"}"));
    
    BOOST_CHECK_THROW(CallRPC("createrawtransaction [{\"txid\":\"a3b807410df0b60fcb9736768df5823938b2f838694939ba45f3c0a1bff150ed\",\"vout\":0}] {\"somedata\":\"68656c6c6f776f726c64\"}"), std::runtime_error);
    
    BOOST_CHECK_THROW(CallRPC("createrawtransaction [{\"txid\":\"a3b807410df0b60fcb9736768df5823938b2f838694939ba45f3c0a1bff150ed\",\"vout\":0}] {\"data\":\"12345\"}"), std::runtime_error);
    BOOST_CHECK_THROW(CallRPC("createrawtransaction [{\"txid\":\"a3b807410df0b60fcb9736768df5823938b2f838694939ba45f3c0a1bff150ed\",\"vout\":0}] {\"data\":\"12345g\"}"), std::runtime_error);
    
    BOOST_CHECK_NO_THROW(CallRPC("createrawtransaction [{\"txid\":\"a3b807410df0b60fcb9736768df5823938b2f838694939ba45f3c0a1bff150ed\",\"vout\":0}] {\"data\":\"010203040506070809101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960616263646566676869707172737475767778798081\"}"));
}
BOOST_AUTO_TEST_CASE(rpc_format_monetary_values)
{
    BOOST_CHECK(ValueFromAmount(0LL).write() == "0.00000000");
    BOOST_CHECK(ValueFromAmount(1LL).write() == "0.00000001");
    BOOST_CHECK(ValueFromAmount(17622195LL).write() == "0.17622195");
    BOOST_CHECK(ValueFromAmount(50000000LL).write() == "0.50000000");
    BOOST_CHECK(ValueFromAmount(89898989LL).write() == "0.89898989");
    BOOST_CHECK(ValueFromAmount(100000000LL).write() == "1.00000000");
    BOOST_CHECK(ValueFromAmount(2099999999999990LL).write() == "20999999.99999990");