Editorial: Add negative sign when value is 0

To handle the case:
```js
new Intl.DurationFormat("en", {hoursDisplay: "always"}).format({hours: 0, seconds: -1})
```
which should output `"-0 hr, 1 sec"`.

spec.emu

@@ -300,6 +300,8 @@ contributors: Ujjwal Sharma, Younies Mahmoud
  1. If _value_ is not 0 or _display_ is not *"auto"* or _displayRequired_ is *"true"*, then
  1. If _displayNegativeSign_ is *true*, then
  1. Set _displayNegativeSign_ to *false*.
+ 1. If _value_ is 0 and DurationRecordSign(_duration_) is -1, then
+ 1. Set _value_ to ~negative-zero~.
  1. Else,
  1. Perform ! CreateDataPropertyOrThrow(_nfOpts_, *"signDisplay"*, *"never"*).
  1. Perform ! CreateDataPropertyOrThrow(_nfOpts_, *"numberingSystem"*, _durationFormat_.[[NumberingSystem]]).