LibJS: Ensure NudgeToCalendarUnit is given a non-zero duration sign

Otherwise, we trip internal Temporal spec assertions.

This is an editorial change in the Temporal spec. See:
https://github.com/tc39/proposal-temporal/commit/30f8575

Libraries/LibJS/Runtime/Temporal/Duration.cpp

@@ -1378,8 +1378,8 @@ ThrowCompletionOr<Crypto::BigFraction> total_relative_duration(VM& vm, InternalD
 {
     // 1. If IsCalendarUnit(unit) is true, or timeZone is not UNSET and unit is DAY, then
     if (is_calendar_unit(unit) || (time_zone.has_value() && unit == Unit::Day)) {
-        // a. Let sign be InternalDurationSign(duration).
-        auto sign = internal_duration_sign(duration);
+        // a. If InternalDurationSign(duration) < 0, let sign be -1; else let sign be 1.
+        auto sign = internal_duration_sign(duration) < 0 ? -1 : 1;
 
         // b. Let record be ? NudgeToCalendarUnit(sign, duration, destEpochNs, isoDateTime, timeZone, calendar, 1, unit, TRUNC).
         auto record = TRY(nudge_to_calendar_unit(vm, sign, duration, dest_epoch_ns, iso_date_time, time_zone, calendar, 1, unit, RoundingMode::Trunc));

Libraries/LibJS/Tests/builtins/Temporal/Duration/Duration.prototype.total.js

@@ -17,6 +17,14 @@ describe("correct behavior", () => {
         }
     });
 
+    test("blank duration", () => {
+        const duration = new Temporal.Duration();
+        const relativeTo = new Temporal.ZonedDateTime(1n, "UTC");
+
+        const result = duration.total({ unit: "years", relativeTo: relativeTo });
+        expect(result).toBe(0);
+    });
+
     test("relative to plain date", () => {
         const duration = new Temporal.Duration(0, 0, 0, 31);