Prevents crashes in Neochat and other kirigami-based applications.
https://bugreports.qt.io/browse/QTBUG-129500
https://codereview.qt-project.org/c/qt/qtdeclarative/+/595278
--- a/src/quick/items/qquickitem.cpp
+++ b/src/quick/items/qquickitem.cpp
@@ -8757,7 +8757,8 @@
     QPointF p = mapToScene(point);
     if (item) {
-        const QQuickWindow *itemWindow = item->window();
-        if (itemWindow != nullptr && itemWindow != window())
-            p = itemWindow->mapFromGlobal(window()->mapToGlobal(p));
+        const auto *itemWindow = item->window();
+        const auto *thisWindow = window();
+        if (thisWindow && itemWindow && itemWindow != thisWindow)
+            p = itemWindow->mapFromGlobal(thisWindow->mapToGlobal(p));
 
         p = item->mapFromScene(p);
@@ -8864,7 +8865,8 @@
     if (item) {
         p = item->mapToScene(point);
-
-        if (item->window() != window())
-            p = window()->mapFromGlobal(item->window()->mapToGlobal(p));
+        const auto *itemWindow = item->window();
+        const auto *thisWindow = window();
+        if (thisWindow && itemWindow && itemWindow != thisWindow)
+            p = thisWindow->mapFromGlobal(itemWindow->mapToGlobal(p));
     }
     return mapFromScene(p);
--- a/tests/auto/quick/qquickitem2/data/mapCoordinatesWithWindows.qml
+++ b/tests/auto/quick/qquickitem2/data/mapCoordinatesWithWindows.qml
@@ -49,3 +49,14 @@
         }
     }
+
+    property Item itemWithoutWindowA: Item {
+        x: 20; y: 20
+    }
+    property Item itemWithoutWindowB: Item {
+        x: 40; y: 40
+        Item {
+            objectName: "childItemWithoutWindow"
+            x: 30; y: 30
+        }
+    }
 }
--- a/tests/auto/quick/qquickitem2/tst_qquickitem.cpp
+++ b/tests/auto/quick/qquickitem2/tst_qquickitem.cpp
@@ -2884,4 +2884,31 @@
     QCOMPARE(childItemInChildWindow->mapFromItem(childItemInOtherWindow, {0, 0}),
         globalItemOffset(childItemInOtherWindow, childItemInChildWindow));
+
+    // If one or both of the items are not in a scene (yet), they are assumed
+    // to eventually be in the same scene.
+
+    auto *itemWithoutWindowA = root->property("itemWithoutWindowA").value<QQuickItem*>();
+    QVERIFY(itemWithoutWindowA);
+    auto *itemWithoutWindowB = root->property("itemWithoutWindowB").value<QQuickItem*>();
+    QVERIFY(itemWithoutWindowB);
+    auto *childItemWithoutWindow = itemWithoutWindowB->findChild<QQuickItem*>("childItemWithoutWindow");
+    QVERIFY(childItemWithoutWindow);
+
+    QPoint itemWithoutWindowAPos = itemWithoutWindowA->position().toPoint();
+    QPoint itemWithoutWindowBPos = itemWithoutWindowB->position().toPoint();
+
+    QCOMPARE(itemWithoutWindowA->mapToItem(childItemWithoutWindow, {0, 0}),
+        itemWithoutWindowAPos - (itemWithoutWindowBPos + childItemWithoutWindow->position()));
+    QCOMPARE(itemWithoutWindowA->mapFromItem(childItemWithoutWindow, {0, 0}),
+        (itemWithoutWindowBPos + childItemWithoutWindow->position()) - itemWithoutWindowAPos);
+
+    QCOMPARE(itemWithoutWindowA->mapToItem(childItem, {0, 0}),
+        itemWithoutWindowAPos - itemPos);
+    QCOMPARE(itemWithoutWindowA->mapFromItem(childItem, {0, 0}),
+        itemPos - itemWithoutWindowAPos);
+    QCOMPARE(childItem->mapToItem(itemWithoutWindowA, {0, 0}),
+        itemPos - itemWithoutWindowAPos);
+    QCOMPARE(childItem->mapFromItem(itemWithoutWindowA, {0, 0}),
+        itemWithoutWindowAPos - itemPos);
 }