LibJS: Correctly handle mixing +0 and -0 in Math.{min,max}()

The native C++ < and > operators won't handle this correctly, so the
result was different depending on the order of arguments. This is now
fixed by explicitly checking for positive and negative zero values.

Fixes #6589.

Userland/Libraries/LibJS/Runtime/MathObject.cpp

@@ -157,7 +157,8 @@ JS_DEFINE_NATIVE_FUNCTION(MathObject::max)
         auto cur = vm.argument(i).to_number(global_object);
         if (vm.exception())
             return {};
-        max = Value(cur.as_double() > max.as_double() ? cur : max);
+        if ((max.is_negative_zero() && cur.is_positive_zero()) || cur.as_double() > max.as_double())
+            max = cur;
     }
     return max;
 }
@@ -174,7 +175,8 @@ JS_DEFINE_NATIVE_FUNCTION(MathObject::min)
         auto cur = vm.argument(i).to_number(global_object);
         if (vm.exception())
             return {};
-        min = Value(cur.as_double() < min.as_double() ? cur : min);
+        if ((min.is_positive_zero() && cur.is_negative_zero()) || cur.as_double() < min.as_double())
+            min = cur;
     }
     return min;
 }

Userland/Libraries/LibJS/Tests/builtins/Math/Math.max.js

@@ -5,6 +5,8 @@ test("basic functionality", () => {
     expect(Math.max(1)).toBe(1);
     expect(Math.max(2, 1)).toBe(2);
     expect(Math.max(1, 2, 3)).toBe(3);
+    expect(Math.max(-0, 0)).toBe(0);
+    expect(Math.max(0, -0)).toBe(0);
     expect(Math.max(NaN)).toBeNaN();
     expect(Math.max("String", 1)).toBeNaN();
 });

Userland/Libraries/LibJS/Tests/builtins/Math/Math.min.js

@@ -4,6 +4,8 @@ test("basic functionality", () => {
     expect(Math.min(1)).toBe(1);
     expect(Math.min(2, 1)).toBe(1);
     expect(Math.min(1, 2, 3)).toBe(1);
+    expect(Math.min(-0, 0)).toBe(-0);
+    expect(Math.min(0, -0)).toBe(-0);
     expect(Math.min(NaN)).toBeNaN();
     expect(Math.min("String", 1)).toBeNaN();
 });