`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.
{
    int64_t s64t = -9223372036854775807LL; 
    uint64_t u64t = 18446744073709551615ULL; 
    BOOST_CHECK(strprintf("%s %d %s", B, s64t, E) == B" -9223372036854775807 " E);
    BOOST_CHECK(strprintf("%s %u %s", B, u64t, E) == B" 18446744073709551615 " E);
    BOOST_CHECK(strprintf("%s %x %s", B, u64t, E) == B" ffffffffffffffff " E);
    size_t st = 12345678; 
    ssize_t sst = -12345678; 
    BOOST_CHECK(strprintf("%s %d %s", B, sst, E) == B" -12345678 " E);
    BOOST_CHECK(strprintf("%s %u %s", B, st, E) == B" 12345678 " E);
    BOOST_CHECK(strprintf("%s %x %s", B, st, E) == B" bc614e " E);
    ptrdiff_t pt = 87654321; 
    ptrdiff_t spt = -87654321; 
    BOOST_CHECK(strprintf("%s %d %s", B, spt, E) == B" -87654321 " E);
    BOOST_CHECK(strprintf("%s %u %s", B, pt, E) == B" 87654321 " E);
    BOOST_CHECK(strprintf("%s %x %s", B, pt, E) == B" 5397fb1 " E);
}
#undef B
#undef E
/* Check for mingw/wine issue #3494
 * Remove this test before time.ctime(0xffffffff) == 'Sun Feb  7 07:28:15 2106'
 */
BOOST_AUTO_TEST_CASE(gettime)