Don't create platform window for QWindows when calling setVisible(false)

We can defer the creation until the window is shown.

Change-Id: I3d5b45ae59ee0925996cf12cd46dd574c8c6ef95
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@qt.io>

src/gui/kernel/qwindow.cpp

@@ -532,7 +532,9 @@ void QWindow::setVisible(bool visible)
         // can defer creation until the parent is created or we're re-parented.
         if (parent() && !parent()->handle())
             return;
-        else
+
+        // We only need to create the window if it's being shown
+        if (visible)
             create();
     }
 
@@ -574,7 +576,8 @@ void QWindow::setVisible(bool visible)
         d->applyCursor();
 #endif
 
-    d->platformWindow->setVisible(visible);
+    if (d->platformWindow)
+        d->platformWindow->setVisible(visible);
 
     if (!visible) {
         QHideEvent hideEvent;

tests/auto/gui/kernel/qwindow/tst_qwindow.cpp

@@ -56,6 +56,7 @@ private slots:
     void create();
     void setParent();
     void setVisible();
+    void setVisibleFalseDoesNotCreateWindow();
     void eventOrderOnShow();
     void resizeEventAfterResize();
     void exposeEventOnShrink_QTBUG54040();
@@ -234,6 +235,16 @@ void tst_QWindow::setVisible()
     QVERIFY(QTest::qWaitForWindowExposed(&i));
 }
 
+void tst_QWindow::setVisibleFalseDoesNotCreateWindow()
+{
+    QWindow w;
+    QVERIFY(!w.handle());
+    w.setVisible(false);
+    QVERIFY2(!w.handle(), "Hiding a non-created window doesn't create it");
+    w.setVisible(true);
+    QVERIFY2(w.handle(), "Showing a non-created window creates it");
+}
+
 void tst_QWindow::mapGlobal()
 {
     QWindow a;