`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.
auto v1 = Vector(t1);
    BOOST_CHECK_EQUAL(v1.size(), 1U);
    BOOST_CHECK(v1[0].origin == &t1);
    BOOST_CHECK_EQUAL(v1[0].copies, 1);
    auto v2 = Vector(std::move(t2));
    BOOST_CHECK_EQUAL(v2.size(), 1U);
    BOOST_CHECK(v2[0].origin == &t2);
    BOOST_CHECK_EQUAL(v2[0].copies, 0);
    auto v3 = Vector(t1, std::move(t2));
    BOOST_CHECK_EQUAL(v3.size(), 2U);
    BOOST_CHECK(v3[0].origin == &t1);
    BOOST_CHECK(v3[1].origin == &t2);
    BOOST_CHECK_EQUAL(v3[0].copies, 1);
    BOOST_CHECK_EQUAL(v3[1].copies, 0);
    auto v4 = Vector(std::move(v3[0]), v3[1], std::move(t3));
    BOOST_CHECK_EQUAL(v4.size(), 3U);
    BOOST_CHECK(v4[0].origin == &t1);
    BOOST_CHECK(v4[1].origin == &t2);
    BOOST_CHECK(v4[2].origin == &t3);
    BOOST_CHECK_EQUAL(v4[0].copies, 1);
    BOOST_CHECK_EQUAL(v4[1].copies, 1);
    BOOST_CHECK_EQUAL(v4[2].copies, 0);
    auto v5 = Cat(v1, v4);
    BOOST_CHECK_EQUAL(v5.size(), 4U);
    BOOST_CHECK(v5[0].origin == &t1);
    BOOST_CHECK(v5[1].origin == &t1);
    BOOST_CHECK(v5[2].origin == &t2);
    BOOST_CHECK(v5[3].origin == &t3);
    BOOST_CHECK_EQUAL(v5[0].copies, 2);
    BOOST_CHECK_EQUAL(v5[1].copies, 2);