`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.
vin.push_back(in);
    }
    entry.pushKV("vin", vin);
    UniValue vout(UniValue::VARR);
    for (unsigned int i = 0; i < tx.vout.size(); i++) {
        const CTxOut& txout = tx.vout[i];
        UniValue out(UniValue::VOBJ);
        out.pushKV("value", ValueFromAmount(txout.nValue));
        out.pushKV("n", (int64_t)i);
        UniValue o(UniValue::VOBJ);
        ScriptPubKeyToUniv(txout.scriptPubKey, o, true);
        out.pushKV("scriptPubKey", o);
        vout.push_back(out);
        if (calculate_fee) {
            amt_total_out += txout.nValue;
        }
    }
    entry.pushKV("vout", vout);
    if (calculate_fee) {
        const CAmount fee = amt_total_in - amt_total_out;
        CHECK_NONFATAL(MoneyRange(fee));
        entry.pushKV("fee", ValueFromAmount(fee));
    }
    if (!hashBlock.IsNull())
        entry.pushKV("blockhash", hashBlock.GetHex());
    if (include_hex) {
        entry.pushKV("hex", EncodeHexTx(tx, serialize_flags)); 
    }
}