`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 uint32_t u32 = fuzzed_data_provider.ConsumeIntegral<uint32_t>();
    const int32_t i32 = fuzzed_data_provider.ConsumeIntegral<int32_t>();
    const uint16_t u16 = fuzzed_data_provider.ConsumeIntegral<uint16_t>();
    const int16_t i16 = fuzzed_data_provider.ConsumeIntegral<int16_t>();
    const uint8_t u8 = fuzzed_data_provider.ConsumeIntegral<uint8_t>();
    const int8_t i8 = fuzzed_data_provider.ConsumeIntegral<int8_t>();
    
    
    const char ch = fuzzed_data_provider.ConsumeIntegral<char>();
    const bool b = fuzzed_data_provider.ConsumeBool();
    const Consensus::Params& consensus_params = Params().GetConsensus();
    (void)CheckProofOfWork(u256, u32, consensus_params);
    if (u64 <= MAX_MONEY) {
        const uint64_t compressed_money_amount = CompressAmount(u64);
        assert(u64 == DecompressAmount(compressed_money_amount));
        static const uint64_t compressed_money_amount_max = CompressAmount(MAX_MONEY - 1);
        assert(compressed_money_amount <= compressed_money_amount_max);
    } else {
        (void)CompressAmount(u64);
    }
    static const uint256 u256_min(uint256S("0000000000000000000000000000000000000000000000000000000000000000"));
    static const uint256 u256_max(uint256S("ffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff"));
    const std::vector<uint256> v256{u256, u256_min, u256_max};
    (void)ComputeMerkleRoot(v256);
    (void)CountBits(u64);
    (void)DecompressAmount(u64);
    (void)FormatISO8601Date(i64);
    (void)FormatISO8601DateTime(i64);
    
    if (i64 != std::numeric_limits<int64_t>::min()) {