`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.
class CTransaction;
struct CMutableTransaction;
class uint256;
class UniValue;
class CTxUndo;
CScript ParseScript(const std::string& s);
std::string ScriptToAsmStr(const CScript& script, const bool fAttemptSighashDecode = false);
[[nodiscard]] bool DecodeHexTx(CMutableTransaction& tx, const std::string& hex_tx, bool try_no_witness = false, bool try_witness = true);
[[nodiscard]] bool DecodeHexBlk(CBlock&, const std::string& strHexBlk);
bool DecodeHexBlockHeader(CBlockHeader&, const std::string& hex_header);
/**
 * Parse a hex string into 256 bits
 * @param[in] strHex a hex-formatted, 64-character string
 * @param[out] result the result of the parsing
 * @returns true if successful, false if not
 *
 * @see ParseHashV for an RPC-oriented version of this
 */
bool ParseHashStr(const std::string& strHex, uint256& result);
std::vector<unsigned char> ParseHexUV(const UniValue& v, const std::string& strName);
int ParseSighashString(const UniValue& sighash);
UniValue ValueFromAmount(const CAmount& amount);
std::string FormatScript(const CScript& script);
std::string EncodeHexTx(const CTransaction& tx, const int serializeFlags = 0);
std::string SighashToStr(unsigned char sighash_type);
void ScriptPubKeyToUniv(const CScript& scriptPubKey, UniValue& out, bool fIncludeHex);
void ScriptToUniv(const CScript& script, UniValue& out, bool include_address);
void TxToUniv(const CTransaction& tx, const uint256& hashBlock, UniValue& entry, bool include_hex = true, int serialize_flags = 0, const CTxUndo* txundo = nullptr);
#endif