Fix Math.sumPrecise to correctly return -0 for empty arrays

- Empty arrays should always return -0 per spec
- Separate logic for empty vs all-zeros cases
- Matches behavior of Hermes implementation

Author: anivar

rhino/src/main/java/org/mozilla/javascript/NativeMath.java

@@ -781,8 +781,12 @@ private static Object sumPrecise(
 
         // Handle all zeros (including empty input)
         if (allZeros) {
-            // Empty input or all zeros - return -0 for empty, appropriate zero for actual zeros
-            return ScriptRuntime.wrapNumber(partialsSize == 0 || hasNegativeZero ? -0.0 : 0.0);
+            // Empty input should always return -0
+            if (partialsSize == 0) {
+                return ScriptRuntime.wrapNumber(-0.0);
+            }
+            // All zeros - return -0 if any negative zeros, otherwise +0
+            return ScriptRuntime.wrapNumber(hasNegativeZero ? -0.0 : 0.0);
         }
 
         // Sum partials