`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 auto& it = mapSigHashTypes.find(sighash_type);
    if (it == mapSigHashTypes.end()) return "";
    return it->second;
}
/**
 * Create the assembly string representation of a CScript object.
 * @param[in] script    CScript object to convert into the asm string representation.
 * @param[in] fAttemptSighashDecode    Whether to attempt to decode sighash types on data within the script that matches the format
 *                                     of a signature. Only pass true for scripts you believe could contain signatures. For example,
 *                                     pass false, or omit the this argument (defaults to false), for scriptPubKeys.
 */
std::string ScriptToAsmStr(const CScript& script, const bool fAttemptSighashDecode)
{
    std::string str;
    opcodetype opcode;
    std::vector<unsigned char> vch;
    CScript::const_iterator pc = script.begin();
    while (pc < script.end()) {
        if (!str.empty()) {
            str += " ";
        }
        if (!script.GetOp(pc, opcode, vch)) {
            str += "[error]";
            return str;
        }
        if (0 <= opcode && opcode <= OP_PUSHDATA4) {