QmlCompiler: Fix code for object literal generation

We have to use the arguments as base for the run time calculated
members, not the argument count.

Amends commit f839171eef.

Pick-to: 6.7
Fixes: QTBUG-123613
Change-Id: I3ddc8bc459618bd9a9436d3616c444bf218463a3
Reviewed-by: Olivier De Cannière <olivier.decanniere@qt.io>
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>

src/qmlcompiler/qqmljscodegenerator.cpp

@@ -2562,7 +2562,7 @@ void QQmlJSCodeGenerator::generate_DefineObjectLiteral(int internalClassId, int
         }
 
         for (int i = classSize; i < argc; i += 3) {
-            const int nameArg = argc + i + 1;
+            const int nameArg = args + i + 1;
             m_body += u"{ "_s
                     + conversion(
                               registerType(nameArg),
@@ -2570,7 +2570,7 @@ void QQmlJSCodeGenerator::generate_DefineObjectLiteral(int internalClassId, int
                               consumedRegisterVariable(nameArg))
                     + u", "_s;
 
-            const int valueArg = argc + i + 2;
+            const int valueArg = args + i + 2;
             m_body += convertStored(
                               registerType(valueArg).storedType(),
                               propType,

tests/auto/qml/qmlcppcodegen/data/variantMap.qml

@@ -5,6 +5,7 @@ QtObject {
     property Component shadowable: QtObject {}
     property B b: B { id: theB }
     property rect r: theB.r
+    property var v: { "1": null, "25": undefined, "19": "19" }
 
     property Component c: Component {
         id: unshadowable

tests/auto/qml/qmlcppcodegen/tst_qmlcppcodegen.cpp

@@ -4937,6 +4937,14 @@ void tst_QmlCppCodegen::variantMap()
 
     QCOMPARE(o->objectName(), "a b"_L1);
     QCOMPARE(o->property("r"), QVariant::fromValue(QRectF(12, 13, 14, 15)));
+
+    const QVariantMap expected = QVariantMap {
+        { u"1"_s, QVariant::fromValue<std::nullptr_t>(nullptr) },
+        { u"19"_s, QVariant::fromValue(u"19"_s) },
+        { u"25"_s, QVariant() }
+    };
+
+    QCOMPARE(o->property("v").toMap(), expected);
 }
 
 void tst_QmlCppCodegen::voidConversion()