`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.
{
    
    UniValue r;
    BOOST_CHECK_THROW(CallRPC("getrawtransaction"), std::runtime_error);
    BOOST_CHECK_THROW(CallRPC("getrawtransaction not_hex"), std::runtime_error);
    BOOST_CHECK_THROW(CallRPC("getrawtransaction a3b807410df0b60fcb9736768df5823938b2f838694939ba45f3c0a1bff150ed not_int"), std::runtime_error);
    BOOST_CHECK_THROW(CallRPC("createrawtransaction"), std::runtime_error);
    BOOST_CHECK_THROW(CallRPC("createrawtransaction null null"), std::runtime_error);
    BOOST_CHECK_THROW(CallRPC("createrawtransaction not_array"), std::runtime_error);
    BOOST_CHECK_THROW(CallRPC("createrawtransaction {} {}"), std::runtime_error);
    BOOST_CHECK_NO_THROW(CallRPC("createrawtransaction [] {}"));
    BOOST_CHECK_THROW(CallRPC("createrawtransaction [] {} extra"), std::runtime_error);
    BOOST_CHECK_THROW(CallRPC("decoderawtransaction"), std::runtime_error);
    BOOST_CHECK_THROW(CallRPC("decoderawtransaction null"), std::runtime_error);
    BOOST_CHECK_THROW(CallRPC("decoderawtransaction DEADBEEF"), std::runtime_error);
    std::string rawtx = "0100000001a15d57094aa7a21a28cb20b59aab8fc7d1149a3bdbcddba9c622e4f5f6a99ece010000006c493046022100f93bb0e7d8db7bd46e40132d1f8242026e045f03a0efe71bbb8e3f475e970d790221009337cd7f1f929f00cc6ff01f03729b069a7c21b59b1736ddfee5db5946c5da8c0121033b9b137ee87d5a812d6f506efdd37f0affa7ffc310711c06c7f3e097c9447c52ffffffff0100e1f505000000001976a9140389035a9225b3839e2bbf32d826a1e222031fd888ac00000000";
    BOOST_CHECK_NO_THROW(r = CallRPC(std::string("decoderawtransaction ")+rawtx));
    BOOST_CHECK_EQUAL(find_value(r.get_obj(), "size").get_int(), 193);
    BOOST_CHECK_EQUAL(find_value(r.get_obj(), "version").get_int(), 1);
    BOOST_CHECK_EQUAL(find_value(r.get_obj(), "locktime").get_int(), 0);
    BOOST_CHECK_THROW(CallRPC(std::string("decoderawtransaction ")+rawtx+" extra"), std::runtime_error);
    BOOST_CHECK_NO_THROW(r = CallRPC(std::string("decoderawtransaction ")+rawtx+" false"));
    BOOST_CHECK_THROW(r = CallRPC(std::string("decoderawtransaction ")+rawtx+" false extra"), std::runtime_error);
    
    BOOST_CHECK_THROW(CallRPC("sendrawtransaction"), std::runtime_error);
    BOOST_CHECK_THROW(CallRPC("sendrawtransaction null"), std::runtime_error);
    BOOST_CHECK_THROW(CallRPC("sendrawtransaction DEADBEEF"), std::runtime_error);
    BOOST_CHECK_THROW(CallRPC(std::string("sendrawtransaction ")+rawtx+" extra"), std::runtime_error);
}
BOOST_AUTO_TEST_CASE(rpc_togglenetwork)